I have a Chatterbox FRSX2. It works as an intercom for driver & passenger and as bike to bike communicator with other Chatterbox & most other FRS (Family Radio Service) radios.
It can be helmet mounted, kept in a pocket, or mounted like I did HERE
. I made the bar mount, but I believe factory ones might be available.
It can be voice operated, or push to talk with the button on the unit, or with the wired remote button.
Like Mushu said, wind noise can be a problem. I've only used it with a full face helmet. Above 60 or so it can be a little tough to hear well. I haven't used it as just an intercom, but my buddy has and says the wind noise isn't quite as bad then. As an intercom, you only need an additional headset for the passenger, which plugs into the main unit.
The biggest drawback is the price. I got mine from an online dealer for $240, which included the radio unit, power wire and headset extention cord (for use with the bar mount I made).
It will accept other audio devices (such as FM radios or MP3 players) by the aux input plug, and has a cell phone input. (I think
it only works with Nokias though)
The batteries have lasted for an entire days ride, and can be recharged by the charger that plugs into a standard house outlet, or by an optional power cord from the bike.
All in all I'm happy with it. The only problem both my buddy & I have had is when helmet mounted, the mount started to crack. That's why I decided to go with the bar mount and I made an aluminum mount for my buddies helmet.
There are other Chatterbox units which are intercoms only and alot smaller than the intercom/communicator I have.