In fact, TeleTools has an excellent set of controls for any TAPI or SIP device and Visual Studio. The new version has a new set of controls, which is even easier to use for 90% of applications, so you do not need to study a large set of events, methods and properties. The wrapper around TAPI still works too much than a good set of controls that do most of the work for you. Most applications, such as caller ID and dialing, make up just a few lines of code. In addition, ExceleTel is the only telephone company with TeleScope, which is a unique tool for prototyping, registration, training. Logging can save you a lot of time and let you pinpoint what your device / phone line / application is doing.
ExceleTel has been working with TAPI for over a decade and is consulting with manufacturers who write TAPI drivers (TSP) to get their devices to work. You can find a lot of information on www.exceletel.com and you can get more information on tapi for the win32 newsgroup, where we all share information.
FULL DISCLOSURE: Fred works for Teletools (http://www.microsoftfaqs.com/msg/14811958.aspx)
Fred
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