I just invested in an Autocom Pro M1 system. Allows for rider-to-passenger communication, cell phone, audio input (with auto-volume-decrease), as well as bike-to-bike communications with optional FRS radio. Speakers/boom microphone fit inside helmet easily and stay put. Works up to 150 mph apparently, although I've only tested it up to about half that. Makes a big difference for going two-up with the wife, and think it would be very cool for group rides, especially when the groups gets split up.
Mark