Windows CE includes a telephony service provider (TSP) for an AT command-based modem. A Unimodem driver is included with Windows CE. Other TSPs can be written by an independent software vendor.
It is important to remember that a driver is a separate DLL and not part of TAPI. The modem driver translates TAPI function calls into AT commands to configure and dial modems. TAPI manages the application's use of devices, ports, and call traffic.
If you decide to write an application that enables a user to select and dial a phone number through a dialog box, a modem must be attached or built into the device. A user also needs a telephone set connected to the modem. If the Windows CE–based application dials for a user, a user needs to use the phone and talk through the microphone.
The Unimodem file included with Windows CE is called Unimodem.dll. This file is included in the device ROM.