Do you know about some engine or library to work with telephone calls? The target is to make the automatic answers in some cases.
Edit: Can I make a phone answer instead of the owner?
Almost anything to do with a call is handled at a lower level in Android (control of which may not be available to the programmer). The application can go up to the call screen and initiate a call for the user, but that is usually where the control of the application ends.
For accepting calls, there are some applications that may do the necessary things. Check this application here. This is an automatic answering service for Android.