[This is preliminary documentation and subject to change.]
Requirement (Designed for Microsoft® Windows® Logo)
Telephony-centric applications must use the full Windows Telephony API (TAPI) for telephony-related functions. They must not control telephony-related equipment through proprietary interfaces, drivers, or APIs other than TAPI.
In particular, the application must not access a modem by directly opening the serial port using the CreateFile function ("COMx"), although a "Direct to COMx" mode may be available for accessing non-modem devices.