i bought a pair of these a few weeks ago and now after having tested them extensively on various trips can highly recommend them

http://www.interphoneuk.com/

i got mine from http://www.kroozeez.co.uk/ and they gave superb service and next day delivery when i needed it

i have one on my helmet that is paired to my N95 for phone calls and satnav, and it is also paired to the second interphone that my pillion can wear or can be on another bike. if on another bike, as long as you can see the other rider, it pretty much will connect to them.

the good thing about them is that it's on all the time (unless you disconnect with one touch of the big button) and both people can speak at once

it uses more battery power when connected bike to bike, but even riding 300 miles back from the lake district yesterday between 10am and 7pm they were still working so battery life is pretty good (although we did switch them off now and again on some motorway sections).

i have a headset in a schuberth c3 helmet and can hear it no problem at least until 90mph (on a private road ) although in my arai chaser i can't really hear it above about 70mph as the helmet makes too much wind noise)

i've tried other systems based on walkie talkies before, but this is so much better as you can both talk at once (useful if the other person is a woman ). not to be confused with similar devices on the market that are not as good apparently according to the research i did before buying them.

 

seconded