Hello,
I used freepascal to write an usermode usb driver (using libusb) for the topcom butler 4012 voip usb phone.
I also wrote a program that uses linphonecore to make a sip phone controlled by the 4012 (making a quick'n'dirty modification of the h2pas translated linphonecore.h).
Due to the problems I had with fork, I decided to let the program run in the foreground.
In case someone is interested it's available at
http://ventoso.org/luca/topcombutler4012/
In the tarball there's also a simple gui program (made with lazarus) to test the phone.

Bye