communications unit?

Went in today to have the dealership look for a break in the Obus as I replaced the Amp1 and still no radio. The service guy couldn't give me a parts number or description of what a communications unit is only that it would cost $695.00. So I'm betting if I found the parts number I could get it working for half. Can anyone tell me what a communications unit is for a 2003 93ss? I had to get going, but will call the parts guy there and try to get some answers.