如何通过基于Web的php应用程序向isdn phone发送呼叫？

I am looking for a solution for a web based application written in PHP where the users are able to control their isdn phones, primarily sending calls to their phone. I know there is something like Asterik / freepbx but i am not sure wether it's the answer to the task, neither do i know how the setup would be.

Would the client have to install a virtual server with pbx running on their machine? Or can this be achived by some sort of socket interface (TAPI) ?

Any useful hints are appreciated