This library was a commercial product for julmar.com for many years. It is a C++ library designed to help create TAPI 1.x and 2.x service providers. It's quite old and relies on MFC for collections and several other aspects.
An updated library which uses STL (but is still pretty old) is available at https://github.com/markjulmar/tsplib3.
This code comes with no support or promises. I have released it because people have asked for it - but it's too far in my past for me to realistically remember much. However, it had full documentation (contained here).