I have just come back from a little tour of europe using bike to bike communication.
Both bikes are running Autocom Active 7 intercoms (well I think they are Active 7, but they are quite old and they keep updating them and changing names!!
) But they are just the simple bottom of the range items.
They are linked to Kenwood Funky radios (also old and now out of production, but basically cheapish £60 PMR radios) using voice activation. These radios use x3 AA batteries, but I cheated and fitted them with a wooden dummy battery and wired them into a 5V USB transformer. This gives them plenty of power and worked perfectly.
Once they are wired into the bike power you need to fit a GROUND EFFECT ISOLATOR otherwise there is too much hum on the system. I bought these off of eBay for around £3.75. I needed to graft this into the lead from the radio to the Autocom but it wasn't difficult and only involved cutting the audio wires and wiring in the isolator.
Everything was then strapped under the seats and off we went.
On the whole everything was fine and worked well. Had a few problems with power plugs unplugging, but that can all be solved easily and fitted into one box when I have time.
We did have an issue with distance especially in the Alps with a few corners between us. But on the whole I would recommend using them and will look at upgrading to Intaride PMR radios as they are delivered at 0.5 watts but you can unlock them to 4 watts! and fit external aerials! I've been told the position of the aerial is pretty important. If yours in laying flat then it is best that the person you want to talk to is the same.