Is there a way to have a call-in type thing with a shoutcast radio station?

Me and a friend are considering adding a "call-in" section to a webcast radio show. We just aren't quite sure if something like this is even possible. Would I be able to set up a teamspeak server or something then forward the output to the shoutcast stream or something like that?

Or maybe something with VoIP?

I can only tell you how the guys at C.B.S. do it when they're streaming a live dj-set. They hookup a laptop to the output of a mixer and stream that. Because they're using a mixer they can just about mix anything into the stream.

Maybe you could use a telephone microphone and use the mic channel on a mixer?