How to implement TAPI in asp.net

Question

I know that TAPI is a standard program(dll)...But i would like to know how to implement it ?? Is it a built in dll in .net 2.0 or 3.5?? Should we need to download from outside If so how to import it ?? Does this TAPI helps in finding solution for tracking the phone calls and dial digits on the computer??

Please help me out in finding the solution