in the following detailed description , a plurality of specific details , such as methods for establishing calls between a user and a customer service agent and particular javascript commands for implementing various functions , are set forth in order to provide a thorough understanding of the preferred embodiments discussed below . the details discussed in connection with the preferred embodiments should not be understood to limit the present invention . furthermore , for ease of understanding , certain method steps are delineated as separate steps ; however , these steps should not be construed as necessarily distinct nor order dependent in their performance . the embodiments discussed below involve the provision of a call tracking service provided by a third party service provider to the operator of a merchant website that receives referrals from one or more other websites operated by parties unrelated to any other party involved in the transaction . the third party service provider provides javascript code to the merchant website , provides the dynamically allocated telephone numbers and the telephone service , and reports the call tracking information to the owner of the merchant website . however , it should be understood that the call tracking and dynamic telephone number allocation methods discussed herein can also be performed by the operator of the merchant website . fig1 illustrates a system 100 for call reporting according to an embodiment of the present invention . the system 100 includes a search engine server 110 to which an end user pc 120 equipped with a browser ( e . g ., internet explorer , firefox , etc .) can connect via internet 130 in order to locate information . the search engine server 110 may be , for example a google server . the end user associated with end user pc 120 may enter keywords as search terms at the search engine server 110 in order to locate desired information concerning a product or service the end user wishes to purchase . in response to the user &# 39 ; s request , the search engine server 110 may list one or more urls containing the keyword , including a url associated with merchant web server 112 . ( although a search engine server is used in this example , it should be understood that the techniques discussed herein can be used in connection with any server that is capable of providing a referring link to merchant web server 112 ). merchant web server 112 provides one or more web pages including at least one pstn ( public switched telephone network ) telephone number that the end user may call to obtain additional information about the products and services described on the website associated with merchant web server 112 . the end user may then choose to call the phone number provided on merchant web server 112 using end user phone 170 to contact a customer service agent at phone 180 via the pstn 160 in order to obtain the desired additional information and / or place an order for the products or services . also connected to the internet 130 is a call server 140 . the call server 140 is in communication with a first voip ( voice over internet protocol ) gateway 150 and a second voip gateway 151 ( two voip gateways are shown in fig1 , but additional voip gateways are present in other embodiments ). the voip gateways , which are available from a variety of sources such as cisco ™, have the ability to convert a call from the pstn ( public switched telephone network ) 160 to a voip ( voice over internet protocol ) phone call . the call server 140 controls the voip gateways 150 , 151 such that when an incoming pstn call is received via the first voip gateway 150 , the call server 140 determines the did ( direct inward dialing ) number representing the phone number dialed by the calling party ( which is dynamically allocated by the call server 140 as discussed in further detail below ), determines a pstn telephone number to which the incoming call should be directed , controls the second voip gateway 150 to place an outbound pstn call to the pstn telephone number determined in the previous step , and bridges the outbound call to the inbound call by connecting the voip input of one gateway to the voip output of the other gateway and vice versa as illustrated symbolically in fig1 by the dashed line between gateways 150 , 151 . although voip gateways 150 , 151 are illustrated in the embodiment of fig1 , it should be understood that any call processing equipment that is capable of receiving an incoming pstn call on one telephone number and redirecting the call to a second pstn telephone number may be used in place of the voip gateways 150 , 151 ( e . g ., a personal branch exchange with remote call forwarding capability ), and that the destination could go directly to the desired location skipping remote call forwarding entirely . operation of the system 100 of fig1 will now be discussed with reference to fig2 , 3 and 4 . fig2 is a flowchart 200 illustrating processing that occurs at the end user pc 120 . the process begins with the downloading of javascript code from the call server 140 at step 202 when a web page from merchant web server 112 is accessed by the end user pc 120 via a referral from the search engine server 110 . in some embodiments , a web page served by the merchant web server 112 may include a single line of javascript code that will download other javascript commands to facilitate call tracking . an example of such a line of code is : this line of code is preferably placed in the webpage &# 39 ; s header , footer , or some other location in the webpage which will ensure that the line of code is always executed when the web page is loaded to the end user pc 120 . this code results in the download of additional javascript code / commands from the call server 140 . ( in the description herein , “ estara ” refers to the assignee of the present application which acts as a third party call tracking service provider ). in applications in which a third party is providing the call tracking service to a merchant , providing the merchant with a single line of code to include on its web pages simplifies administration of the web page for the merchant . alternatively , the downloaded javascript code can be included in the web page , thereby avoiding the necessity of downloading the code after the web page from the merchant server 110 is loaded . the use of javascript commands is preferable because it allows the collection and transmission of data from a web page on the user &# 39 ; s pc 120 to a third party server 140 outside the domain of the merchant web server 110 without the use of a plug - in or other means that would require the user to perform some action . the javascript commands downloaded at step 202 function to retrieve the url of the referring web page at step 204 . the availability of a referring url is well known and widely supported . the referring url is examined to determine whether search parameters are present at step 206 . as is well known to those of ordinary skill in the art , the referring url from a search engine such as google can include the keywords and other information . for example , a search for the term “ softphone ” on the google search engine returns a list of hits including the estara webpage . the referring url in such a case takes the form of http :// www . google . com / search ? hl = en & amp ; q = softphone & amp ; btng = search , which identifies the website as google . com , identifies the keyword as “ softphone ” and indicates that the url was identified as a result of the user hitting the “ search ” button on the google website . in some various embodiments the keyword “ softphone ,” the identification of the referring website “ google . com ,” or both , constitute tracking parameters that are tracked for any phone call that results from the referral by the search engine server 110 to the merchant web server 112 . if search parameters are present in the referring url at step 206 , the tracking parameters are retrieved from the referring url at step 212 . if there are no tracking parameters in the referring url at step 206 , the current url ( i . e ., the url of the web page on the merchant server 112 currently being viewed on the end user pc 120 ) is retrieved at step 208 and any tracking parameter ( s ) in the current url are retrieved at step 210 . after retrieval of the tracking parameters from the current url at step 210 or the referring url at step 212 , the web page is searched for additional tracking parameters at step 214 . these additional parameters may include , for example , information that identifies the end user . this information may be present in a form on the current web page or in a cookie associated with the web page . such identification information may be used with embodiments in which a phone number is dynamically allocated for each user as discussed in further detail below . the search for additional tracking parameters should be understood to be optional . for example , in embodiments in which the only parameter that is tracked is a keyword , there is no need to search the web page if the keyword is identified in the referring url or the current url . the web page may be searched using techniques similar to those discussed in co - pending , commonly owned u . s . patent application ser . no . 11 / 737 , 729 , entitled “ method and apparatus for web page co - browsing with a standard browser ,” the entire contents of which are hereby incorporated by reference herein . it should also be understood that step 214 may be executed periodically ( e . g ., once every two seconds ) so that any information entered by the user after the web pages initially loads ( e . g ., the user may enter his / her name , address , etc . on a form on the page ) can be captured and sent to the call server 140 after the initial message is sent as discussed in further detail below . next , any phone number present on the current web page is identified at step 216 . this task is preferably performed at the end user pc 120 using javascript regular expressions , for common forms of telephone numbers . however , in some embodiments , a copy of the web page is created and sent to the call server 140 so that the call server 140 can locate any phone numbers . the copy of the web page may be created and sent to the call server 140 using techniques similar to those described in the aforementioned co - pending , commonly owned u . s . patent application . ( it should be understood that step 216 is optional and that no phone number is listed on the web page in some embodiments prior to a phone number being dynamically allocated by the call server 140 and placed on the web page as discussed in further detail below ). next , a message is sent to the call server 140 requesting a tracking phone number and providing the call server with the previously retrieved tracking parameters at step 218 . those of skill in the art will recognize that the tracking parameters and the request for a tracking phone number may be sent in separate messages or in a single message to the call server 140 . the phone number on the web page is replaced with a tracking phone number received from the call server 140 at step 220 . fig3 illustrates the processing performed at the call server 140 upon receipt of the new phone number request / call tracking parameters message sent by the end user pc 120 at step 218 . the message from the end user pc 120 is received at step 302 . the call server 140 checks its existing database to determine if a phone number is currently allocated for the tracking parameters in the message at step 304 . if no phone number is currently allocated for the tracking parameters in the message , an unallocated phone number is retrieved from a pool of unallocated phone numbers at step 306 . the phone number is allocated to the tracking parameter ( s ) and the tracking parameters / phone number pairing along with a destination phone number associated with the pairing are stored in the database along with a time at which the allocation occurred at step 308 . a background process at the call server 140 uses the allocation time stored in the database to determine whether the allocation has exceeded a predetermined time period and , if so , breaks any such allocation and returns the telephone number to the pool of unallocated telephone numbers . if there is an existing phone number allocation at step 304 , the allocation time is updated at step 312 . the allocated phone number is then sent to the end user pc 120 at step 310 . fig4 illustrates the processing performed by the call server 140 when a phone call is received . the phone number associated with an inbound call is determined at step 402 . this determination may be made , for example , by determining the did ( direct inward dialing ) associated with the call in a manner well known to those of skill in the art . other techniques may also be used . the call server 140 then checks its database to determine whether the phone number associated with the incoming call is currently allocated at step 404 . if there is no current allocation , the outbound phone number to which the phone number was previously allocated is retrieved at step 416 . this is done to account for situations in which an end user unexpectedly waits for an amount of time in excess of the predetermined time period in order to place a call . ( alternatively , if a phone call is received on an unallocated phone number , an error may be declared and the phone call may be terminated ). if the phone number is allocated at step 404 , the ani ( automatic number identification ) of the incoming caller is obtained at step 406 . as is well known in the art , the ani identifies the telephone number of the calling party . if the ani matches an ani stored in the call server 140 database for a previous caller on the same telephone number , a check is made to determine whether the time since the previous call has exceeded a threshold at step 410 . this threshold may be the same or different from the threshold discussed above . if the time since the has not exceeded the threshold , the outbound phone number to which the inbound phone number was previously allocated is retrieved at step 414 . otherwise , or if the ani indicates that the inbound caller has not previously called the inbound telephone number , the outbound phone number to which the inbound phone number is currently allocated is retrieved at step 412 . an outbound call to the telephone number retrieved at step 412 , 414 or 416 is placed at step 418 . the inbound and outbound calls are then bridged in the manner described above at step 420 , and a record of the call is stored at step 422 either when the call is first connected or when it is terminated . the call record can include the tracking parameters ( which , as discussed above , can include keyword ( s ), the identity of the referring webpage , the identity of the caller , the ip address of the caller , which web pages the caller visits , etc . ), the time and date , the length of the call , and / or the phone number to which the outbound call was directed . the call record is reported at step 424 . step 424 may be performed on a per - call basis , or may be performed periodically such that information for a plurality of calls is reported . steps 406 , 408 , 410 and 414 discussed above are useful to avoid situations in which an end user initially dials a phone number to reach a party and then calls the same number later after it has been reallocated . this technique is referred to as “ sticky days ” by the assignee of the present invention . this technique is believed to be particularly well suited to situations in which a generic phone number listed on a search engine ( or other ) website is used to point at a highest bidder in a pay per call scenario ( e . g ., the search engine server offers referrals to the highest bidder from among a plurality of web merchants , and the destination phone number at the call server 140 that is associated with the generic phone number listed on the search engine server is changed depending on which web merchant bids the highest amount for the referral ). the use of dynamic number allocation represents a significant improvement over static allocations . while it is possible to statically assign telephone numbers to a small group of keywords , static allocations become impractical when the number of keywords is large . it is not uncommon to have hundreds of keywords , including dozens that may get very little traffic , and the keywords may be utilized in dozens of campaigns . there are a finite number of telephone numbers available , and reserving a dedicated telephone number costs money . both available phone numbers and available funds would be depleted quickly using a static allocation scheme of any size . the use of dynamic allocation addresses this issue to a large extent . however , the use of dynamic number allocation does involve some tradeoffs . for example , as discussed above , some embodiments simply allocate a phone number to a tracking parameter such as a keyword for some predetermined period of time . in these embodiments , some numbers allocated to popular keywords may stay allocated to the same keyword for long periods of time due to regular usage and updating of the time of allocation as discussed in connection with step 312 of fig3 . other phone numbers allocated to less popular keywords may be frequently returned to the pool of unallocated numbers and reassigned . it is always possible that an end user may decide to call such a number after it has been reallocated to a different keyword and destination telephone number and even after the time threshold of step 410 ( in those embodiments that include this optional processing ) has been exceeded . in such a scenario , a phone call will erroneously be recorded and the end user will erroneously be connected to a party to which they did not wish to speak . the frequency of such an error will increase as the amount of time in which phone number / tracking parameter allocations are maintained is increased , but increasing this time will decrease the number of available telephone numbers thereby increasing the total number of telephone numbers needed and the cost associated therewith . it will be apparent to those of skill in the art that numerous variations in addition to those discussed above are also possible . therefore , while the invention has been described with respect to certain specific embodiments , it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention . it is intended therefore , by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention . furthermore , the purpose of the abstract is to enable the u . s . patent and trademark office and the public generally , and especially the scientists , engineers and practitioners in the art who are not familiar with patent or legal terms or phraseology , to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application . the abstract is not intended to be limiting as to the scope of the present invention in any way .