If they have an API, I'm confident an integration could be created. Or, depending on the complexities of what you actually need, it might be easy enough to build a solution yourself.
I suspect Callscripter has lots of features. The question is what features are you actually using. That will determine whether to build an integration, or replace Callscripter with your own solution. For example, popping a script when a call is answered would be super easy. Collecting the duration of the call for billing purposes, also very straightforward. Building a complete billing system... not so easy.