TAPI 3.x vs. TAPI 2.x

The COM-based telephony API, TAPI 3.x, is available starting with Windows XP. TAPI 3.x provides greatly enhanced development tools for the modern world of communication programming, where a "call" may be a video stream on an IP-based network, and there is no phone set involved in the session. Generally speaking, application writers will find TAPI 3.x provides better support to implement flexible communications controls.

However, TAPI 2.x may be the right choice in some situations. If minor modifications are needed for a legacy application, or there are legacy platforms to support, conversion to the COM API may not be cost effective.