If you are looking at being able to talk to another rider in your group try:
www.collett.mb.com
We have used these for years when snowmobiling. Ours are over 15 years old and still work great. The distance depends on terrian and grounding.........on snowmobiles with the snow insulating you from the ground (depending on depth) we normally get about 2-3 miles distance.
Never had a reason I guess to try them on our atv helmets.
The units attach to the helmet with a sound activated mike, so no need to key anything. You can even hook up a walkman,cd player or i-pod to the unit. Play music and when you speak into the mike the music stops. I think the newer ones even come with blue tooth for a phone.
Great company and great unit.

 

Sorry, try

www.collettcommunicator.com

 

Damn, I'll get it right yet

Collett Electronics - Helmet Communication