i've got the g4 and this is what the box says "4-way intecom conference mode between 2 bikers and their passengers or between 3 separate bikers"
i haven't set it up for the mp3 yet but use the fm reciever and although it's ok, it's reception could be better.
since i've used it, i've recieved two phone calls on it and all i had to do was say answer and turn up the volume to hear who's was calling. i was on the cyclone both times which has a supertrapp and had no issues with hearing or talking. my wife couldn't believe i was on the bike when talking to her. it was also nice not to have to take off the helmet just to make a call to check on something. pulled out the phone, chose the number and done deal.
i've yet to get out with the wife to see how it works but just fulling around with it in the house, it's seems like it was a good move. supposedly after the first of the year, the new g4's will be set up so you can use ear buds in them. but the speakers in them are a lot better than the peace of crap stuff that h-d has for their set ups.