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Telephone Dialer

Windows Mobile 6.5

This code sample is named CeDialer. It demonstrates how to place a modem call using the Telephony API. The Telephony API supports outbound calls, but does not support inbound calls. TAPI also supports installable service providers. The Telephony Service Provider Interface (TSPI) allows you to create telephony service applications that handle function calls from remote applications to carry out and control communications over the telephone network.

To run the code sample


    Microsoft Visual Studio launches and loads the solution.


  3. Deploy the solution (F5).

Using TAPI to make a modem call

A Windows Mobile application that uses a modem must be able to handle tasks such as initializing the modem, opening the line, dialing a phone number, and disconnecting when the session is complete. The following are the main steps and associated functions for dialing a call in CeDialer:

  1. Initializing TAPI (using InitializeTAPI and GetLineInfo).
  2. Opening a line and making the call (using MakePhoneCall).
  3. Cleanup (using CurrentLineClose).
Initializing TAPI

When initializing TAPI, the application must establish a way to communicate between a Windows Embedded CE–based application and TAPI.

The CEDialer InitializeTAPI function
  1. Calls lineInitialize to initialize TAPI.
  2. Calls the custom GetLineInfo function to open the line.
  3. GetLineInfo calls lineNegotiateAPIVersion to find TAPI API version to use.
  4. GetLineInfo calls lineGetDevCaps to obtain information on the line.

The lineInitialize function initializes the application's use of the Tapi.dll for subsequent use. It registers the application-specific notification mechanism and returns the number of line devices available to the application.


To receive status notices, the application must implement a TAPI lineCallbackFunc function to establish a way to communicate with TAPI. An application tells TAPI the address of the callback function in the call to lineInitialize. The callback function is used for notifying applications of changes in the status of calls, lines, and phone devices. TAPI uses the callback function to send messages to the application.


The lineNegotiateAPIVersion function, called by GetLineInfo indicates which version of TAPI the application supports, and negotiates which API version number TAPI should use. The reason for negotiating the TAPI version is to be

sure that the correct protocol is used. New versions might define new features, new fields to data structures, and so on. Version numbers therefore indicate how to interpret various data, structures, and messages. If version ranges do not match, the application and API or service provider versions are incompatible and an error is returned. When the function succeeds, the line data such as permanent identifier, number of addresses, and line name, can be obtained from the LINEDEVCAPS structure.


When an application has initiated and negotiated the API, the application needs to verify if the line is usable and ready for dialing out. The application can do this by checking the values filled into the LINEDEVCAPS structure by calling the lineGetDevCaps function.

The lineGetDevCaps function fills in the LINEDEVCAPS structure, which the telephone service provider defines. The size of the structure might be different for different service providers, and therefore the application must check to see if the buffer size is adequate. To check if the amount of space supplied for the structure is sufficient for the size of the structure of the provider, compare the dwNeededSize and dwTotalSize fields. If the total size is too small, the application needs to pass a larger buffer to the function.

Opening a line and making a call

Once TAPI is initialized using the lineInitialize function, an application needs to get an available line using the lineOpen function. In the CEDialer sample the MakePhoneCall function:

  1. Calls lineOpen to open the line.
  2. Calls lineTranslateAdress to translate the phone number.
  3. Sets up call parameters in LINECALLPARAMS structure. The LINECALLPARAMS structure describes parameters supplied when making calls using lineMakeCall. The LINECALLPARAMS structure is also used as a parameter in other operations.
  4. Calls lineMakeCall.

The lineOpen function opens the specified line device and returns a line handle to the opened line device. This line handle is used in subsequent operations on the line device. Later, when the application is finished using the line device, it can close it with lineClose.

The lineOpen function specifies: A handle to the application registration with TAPI, a value that identifies the line device to be opened. Windows Embedded CE does not support the LINEMAPPER value for the dwDeviceID parameter, a pointer to a line handle loaded with the handle representing the opened line device.

The API version number under which the application and TAPI operate compatibly. This number is obtained by calling the lineNegotiateAPIVersion.

The extension version number under which the application and the service provider operate compatibly. Windows Mobile does not support provider-specific extensions. The dwExtVersion parameter should be set to zero prior to calling the lineOpen function.

User-instance data passed back to the application with each message associated with this line or with addresses or calls on this line. This parameter is not interpreted by the TAPI.

The privilege the application wants for the calls it is notified for. This parameter can be a combination of the LINECALLPRIVILEGE constants.


To place a call, the application must call the lineMakeCall function using the LINECALLPARAMS structure. The CEDialer application provides a dialog box for a user to enter the phone number of their choice. TAPI sends LINE_CALLSTATE messages to indicate the progress of the call. For example, LINE_CALLSTATE indicates states of connection, dialing, proceeding, and so on. The messages vary depending on the type of call and the service provided. The application should not be designed to one type or one special sequence of call states.

During data transfer, TAPI continues to manage the connection, but the application handles data transmission and reception. When the transmission is complete, TAPI returns a LINE_CALLSTATE message, such as one indicating that a remote disconnect has occurred. The CeDialer sample does not handle data transmission.

Each call from a Windows phone is identified by a call handle. A call handle provides a pointer to a value to identify a specific call. TAPI assigns call handles as needed. One call handle exists for every call owned by an application. Certain TAPI functions create new calls. As they do so, they return new call handles to the application.

The MakePhoneCall function demonstrates how the LPCALLPARAMS structure can be filled in to support an outbound call.

After the lineMakeCall function successfully sets up the call, TAPI returns a LINE_REPLY message through the callback function. The LINE_REPLY message also informs the application that the call handle returned by lineMakeCall is valid. This message indicates only that the call has been established at the local end, which is perhaps indicated by a dial tone. The application can then use that line to make outbound calls.


When the application receives a message indicating that the call has ended, the application disconnects the call at the local end with lineDrop. The CEDialer CurrentLineClose function:

  1. Calls linedrop to drop the current call.
  2. Calls lineDeallocateCall to release the call handle for the finished call.
  3. Calls lineClose to close the line connection.
linedrop, lineDeallocateCall, lineclose

When a user ends the call, the application should disconnect and terminate the call with lineDrop call the lineDeallocateCall function to free system-allocated memory related to the call handle. The lineDrop function can also be used to drop a call in progress. To finally close the line, the application should call lineClose.

In Windows Embedded CE, TAPI links to and calls TSPI functions using standard dynamic-link library (DLL) functions.

TAPI uses the Unimodem TSPI by default.

SDK: Windows Mobile Professional SDK and Windows Mobile Standard SDK

Development Environment: Visual Studio 2005 or 2008.

ActiveSync: Version 4.5.

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