the invention will be described in detail with reference to a preferred exemplary embodiment , referring to the accompanying drawing . it is to be noted however that the drawing is purely schematic and not necessarily to scale . the drawing and descriptions are to illustrate at least one principle underlying the invention , not to limit the same in any way . the present invention is only limited by the appended claims . referring to the figure , which is a sequence block diagram of a process 1000 according to an exemplary embodiment of the present invention , the process 1000 can involve a calling party &# 39 ; s domain 100 , and a called party &# 39 ; s domain which is referred to as an overall domain 200 , in the following . the called party is represented by a contact center environment , in the present example . a part of the process 1000 is on the side of the called party &# 39 ; s domain , or overall domain 200 . the overall domain 200 comprises an unmonitored domain 300 and a monitored domain 400 . the unmonitored domain 300 comprises an unmonitored device 500 controlled by an unmonitored application 600 , and the monitored domain 400 comprises a monitored device 700 controlled by a monitored application 800 . the monitored application 800 can be run on a device in the monitored domain 400 ( e . g . the monitored device 700 or another device in the monitored domain ) that has the application stored in its memory for execution by that device via at least one processor of the device . the unmonitored application 600 can be run on a device in the unmonitored domain 300 ( e . g . the unmonitored device 500 or another device in the unmonitored domain ) that has the application stored in its memory for execution by that device via at least one processor of the device . it will be noted that the unmonitored domain 300 may comprise a plurality of unmonitored devices , and the monitored domain 400 may comprise a plurality of monitored devices while in the drawing of the present exemplary embodiment only one unmonitored device 500 and one monitored device 700 are illustrated , for the sake of simplifying the principle underlying the invention . the overall domain 200 may comprise a pbx with monitored devices / extensions , and sip - connected trunks that are not monitored . the unmonitored device 500 may in this case be a sip trunk , the unmonitored application 600 may for example be an ivr application , and the monitored device 700 may be assigned to a contact center agent . the process 1000 comprises a plurality of process steps . numbering of steps is such that a first digit following a step indicator “ s ” indicates the process (“ 1 ” for “ 1000 ”), the second digit indicates the logical ( or physical ) instance where the respective step is located ( e . g ., “ 1 ” for caller 100 , “ 5 ” for unmonitored device 500 , and so on ), and the third and fourth digits indicate a step count in the process . as shown in the figure , process 1000 starts as a caller in the caller domain 100 calls the contact center exemplifying overall domain 200 ( step s 1102 ), and the call arrives at the unmonitored device 500 in unmonitored domain 300 ( step s 1504 ). upon receipt of the call , the unmonitored device 500 transmits a call arrival signal to the unmonitored application 600 controlling it ( step s 1512 ) ( e . g . an application run by the unmonitored device or an application run on another device in the unmonitored domain , which ( in some embodiments ) can be configured to control the unmonitored device ). on receipt of the call arrival signal , the unmonitored application 600 requests a new call context from the monitored domain 400 , by sending a requestcontext message to the monitored application 800 controlling monitored device 700 ) ( e . g . an application run by the monitored device 700 or an application run on another device in the monitored domain , which in some embodiments may be configured to control the monitored device 700 ), said requestcontext message including called , calling , and redirect numbers contained in the call ( step s 1614 . upon receipt of the requestcontext message , the monitored application 800 returns a new call context to the unmonitored application 600 ( step s 1816 ). the context information is now stored and can be referred to ( and additional information can be associated and maintained as part of the call context ). hence , the call now exists within the scope of the monitored application , and can be referred to consistently using the call identifier . to move the call from the unmonitored domain 300 to the monitored domain 400 , the unmonitored application 600 first requests a unique call movement identifier , by sending a requesttransfer message to the monitored application 800 , said requesttransfer message including the call context previously returned in step s 1810 ( step s 1622 ). upon receipt of the requesttransfer message , the monitored application 800 returns a unique number to the unmonitored application 600 ( step s 1824 ). it will be noted that the unique number is generated to uniquely identify the call during this particular moving or transfer operation . the unique number of this invention is denoted by “ uniquenumber ” in the figure . upon receipt of the unique number , the unmonitored application 600 instructs its unmonitored device 500 to move the call to the monitored domain 400 , by sending a transfercall message to the unmonitored device 500 , said transfercall message including the called and calling numbers of the call , and the unique number ( step s 1632 ). it is noted that the unique number is specified in a sip diversion header , and is therefore available when the call is received in the monitored domain . the unique number is thus not used as the target of the transfer . upon receipt of the transfercall message , the unmonitored device 500 moves the call to the monitored device 700 ( step s 1534 ). upon receipt of the call , the monitored device 700 transmits a call arrival signal to the monitored application 800 ( step s 1736 ). upon receipt of the call arrival signal , the monitored application 800 reconciles the call , using the unique number specified in the sip diversion header ( step s 1838 ). by reconciliation , the monitored application 800 determines the call context for the call , i . e ., looks up the previously assigned call context , based on the information signalled when the call arrived at the monitored device 700 , including the unique number . even if not shown in the drawing , when that movement of the call is completed ( which may be recognized and verified by the monitored application 800 and / or unmonitored application 600 , the unique number is discarded , i . e ., becomes free for other use . during the movement , the monitored application 800 and / or unmonitored application 600 ensure that the unique number is not used for any move of any other call at the same time . after a period of time , the call is to be moved back to the unmonitored domain 300 . for that , the monitored application 800 instructs its monitored device 700 to perform transfer of the call , by sending a transfercall message which includes a redirection number rn and a unique number which is newly created for the new movement to uniquely identify this particular call movement and may therefore not be the same number as was previously used , to monitored device 700 ( step s 1824 ). as the monitored device 700 receives the transfercall message , it moves the call to the unmonitored device 500 ( step s 1744 ). in some cases , the unique number may alternatively be the same unique number as transmitted in step s 1824 , but preferably a new unique number would be created . in any case , the unique number is generated to uniquely identify the call , and to uniquely link the identifier to the call context in the monitored domain . in other words , when the call is being moved from the monitored domain to the unmonitored domain , to move the call , the monitored application tells the monitored device to transfer the call to a specific number which contains a prefix followed by the unique number that was just allocated . practically speaking , the prefix is what is actually used to move the call to the unmonitored resource ; the unique number consists of additional digits which can be interpreted by the unmonitored application , and then passed back when asking for the call context . upon receipt of the call , the unmonitored device 500 sends a call arrival signal to its unmonitored application 600 ( step s 1552 ). upon receipt of the call arrival signal , the unmonitored device 600 requests call context from the monitored domain 400 , by sending a requestcontext message to the monitored application 800 , the requestcontext message including calling and redirect number “ rn ” as well as the new unique number , to the monitored application 800 ( step s 1654 ). upon receipt of the requestcontext message , at this instance , the monitored application 800 returns the existing call context of the call to the unmonitored application 600 ( step s 1856 ). in other words , when the call is received by the unmonitored application ( from the monitored domain ), it looks at the information contained within the to header field for the called number . the to header field contains the called number and the called number contains the unique number . in this case , the called number in the to header field is the prefix followed by unique number . so at this point , the called number contains the unique number . again , even if not shown in the drawing , when that movement of the call is completed ( which may be recognized and verified by the monitored application 800 and / or unmonitored application 600 ), the unique number is discarded , i . e ., becomes free for other use . during the movement , the monitored application 800 and / or unmonitored application 600 ensure that the unique number is not used for any move of any other call at the same time . conventionally , calls may be moved from monitored to unmonitored domains and vice versa or between two monitored domains crossing an unmonitored domain , which ends up in the call being divided into multiple contexts . according to the process 1000 described above , unmonitored application 600 is running in the unmonitored domain 300 ( e . g . an unmonitored ivr ). if a new call arrives in the unmonitored domain 300 , the unmonitored application 600 running in the unmonitored domain 300 forwards the called number , the calling number and any redirection numbers to the monitored application 800 running in the monitored domain 400 and queries for a new call context . in order to transfer a call to the monitored domain 400 , the unmonitored application 600 running in the unmonitored domain 300 requests a temporary unique number for this call from the monitored application 800 running in the monitored domain 400 . this unique number is put into the diversion header of a sip message . the monitored application 700 in the monitored domain 400 is now able to identify the call as it arrives in the monitored domain 400 and to assign the correct call context . the other way round , if a call is to be routed from the monitored domain 400 into an unmonitored domain 300 , a ( another ) unique number is appended to a route prefix . the unmonitored application 600 in the unmonitored domain 300 then queries the monitored application 800 in the monitored domain 400 to obtain the existing call context . the solution described above is different from a global call id which cannot be maintained while the call is moved between unmonitored and monitored domains ( and vice versa ), and therefore cannot be used to uniquely identify a call after the call is moved from a monitored domain into an unmonitored domain . use of unique numbers while calls are moved into , out of or across unmonitored domains according to the present invention ensures that a single unique call context per call can be maintained and accessed throughout the call lifecycle . the present invention as exemplified above and claimed makes use of both a called number and information in the diversion header to uniquely identify a call thus allowing the context to be maintained as the call moves between monitored and unmonitored devices that are connected via a sip trunk . a sip diversion header may be used when the call is moved from the unmonitored domain to the monitored domain . if a new call arrives in the unmonitored domain , an application running in the unmonitored domain will query the application running in the monitored domain for a new call context by passing in the called , calling and redirection numbers . to move the call from the unmonitored domain to the monitored domain , the application running in the unmonitored domain will request a temporary unique number from the application running in the monitored domain that will uniquely identify the call when transferring it to the monitored domain . this unique number is used in the diversion header , in particular in the sip diversion header the application running in the monitored domain will use this information to reconcile the call once it physically arrives in the monitored domain . to move the call from the monitored domain back to the unmonitored domain , the application running in the monitored domain will allocate a unique number that is appended to a route prefix that allows the call to be routed to the device in the unmonitored domain . when the call arrives in the unmonitored domain , it queries the application running in the monitored domain for the call context by passing in the called , calling and redirection numbers . since the called number contains the unique number , the existing call context is returned . in summary , embodiments of the invention can use the features of sip trunking in combination with both the “ to ” number and sip diversion header to allow call reconciliation between monitored and unmonitored domains . the ability to maintain the call context while the call physically moves between the monitored and unmonitored domains ensures that the call context is maintained for the life of the call in the overall domain . this also advantageously enables proper statistics and handling of the call . obviously , various applications of the present invention may become apparent to the person skilled in the art , based on the information disclosed in the present specification , which might not be mentioned explicitly but are fully covered by the scope of the present application . in an alternative example , the sip header could be extended to provide an identifier that uniquely identifies the session . it is to be noted that the sip call - id is not appropriate for this use as a two - step transfer would result in a second call - id . in this alternative , instead of using the unique identifier or number as the number that is used to transfer the call to ( or as part of the number to transfer the call to ), it would be specified directly using a new field in the sip header . it is to be noted in this case that , as the sip header is a standard , introducing a proprietary extension to the sip header which is only used or recognized by a few components would limit the applicability of the solution and would therefore require each pbx to be modified appropriately . therefore , a technical feature or several technical features which has / have been disclosed with respect to a single or several embodiments disclosed herein before may be present also in another embodiment except it is / they are specified not to be present or it is impossible for it / them to be present for technical reasons . the invention is generally applicable to any fields of communication . however , embodiments of the invention can be based on elements of the sip , details of which may be referred to according to internet engineering task force ( ietf ) standard recommendation , request for comments 3261 ( i . e . rfc 3261 ). the unique number can be provided differently for different call movements . in other words , the unique number is a temporary number which is used while the call is being moved from the unmonitored domain to the monitored domain ( or vice versa , from the monitored domain to the unmonitored domain ). the unique number is associated with the call context that is generated in the monitored application . the call context contains the called number , calling number , and redirection device information for the call when it arrived in the system . the called number , calling number , and redirection device information may change as the call is moved around . when redirection devices change as the call is moved the unique number may also change as it is generated and allocated for a particular call movement operation , and is only used for that particular movement . if the call needs to be moved again , another unique number will be generated and allocated . in any case , the call context is maintained by the monitored application , and at any one point a call identifier or unique number may be directly mapped to a call context in the monitored application . on the other hand , the call identifier is fixed for the lifecycle of the call and does not change when redirection devices change . as described herein , the unique number can be in the form of a number , by definition . however , any alphanumeric character string may be used to identify a call move , in the sense of the unique number . for example , when the call is moved from the unmonitored to the monitored domain , the telephony platform may expect to receive a numeric identifier in form of the alphanumeric character string . in yet other embodiments , another type of character string may be utilized for the unique number . embodiments of the invention may be modified to account for different sets of criteria . for example , the size and configuration of an unmonitored domain and / or a monitored domain can be any suitable arrangement that may meet a particular set of design criteria or communication services objectives . thus , while certain present preferred embodiments of a communication device , communication system , non - transitory computer readable medium , and methods of making and using the same have been shown and described above , it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims .