VoIP in Linux

Hello, I’m a third year university student in Hong Kong who is working on a final year project named VoIP on the MPC860 Based Embedded Linux System.

Basically what I need to do is to port a VoIP software onto the MPC860 platform, which runs with a PowerPC chip. Therefore I need to have a VoIP software which is capable of running under Linux, and is simple (small in size) because the MPC860 do not have enough RAM.

Is there someone who can tell me where can I find such a software?

Thanks a lot!!