I don't believe there is.

One might think that the COM based API exposed by TAPI v3 would have been an
option with the Runtime Callable Wrappers (RCW) provided by .Net but sadly
that is not a supported scenario:

http://support.microsoft.com/default.aspx?scid=kb;en-us;841712

Just by the way, despite of the official non-support, some posters have
mentioned in the TAPI newsgroup that simple .Net applications can make use
of RCW. FWIW, it might work on the desktop, I wouldn't recommend that in a
server.

Just by the way, the lack of TAPI support in .Net caused one user to write
her own wrapper in C# using interop:

http://www.gotdotnet.com/Community/UserSamples/Details.aspx?SampleGuid=5d893af6-
b340-49d8-9162-b90bf6932414

which covers some but not all of the version 2 API.

Regards,
Will