It really depends on the project. My most recent project has been an attempt to revive some old ISDN videophones I bought and integrating them with a more modern teleconference platform, so it involves all sorts of things, from whats basically a custom PBX to the video call app it will integrate with. For the core, PBX-like part, I was initially looking into Erlang, but after a while decided it might be easier to build on top of the JVM platform.

Oh... that's a huge project to tackle! And really dang cool if you can pull it off!

Do you know for sure the hardware even works? Can you get them to talk to each other? What kind of interface do they have? Do they do ethernet at all?