I used helmet communicators from Collett Electronics for years. I got them 20 years ago, so I'm sure there are better technology alternatives now. I can tell you this, it sure made riding through the woods easier when you could talk to your buddies instead of having to stop at every turn, get off the sled, run over and yell in their ear, and keep going. The signal wasn't as clear as a telephone, you had to talk loud and slow to really understand, unless you were sitting still like at a trail crossing. They are voice activated, so I would blow a puff of air into the mic to get it going before talking, otherwise they would miss the first word. After I put on my PSI pipes, my buddies couldn't hear me anyways. They can also be annoying. There were times that I just turned them off so I didn't have to listen to the chatter. My wife and I went riding one Christmas Eve and she wanted me to sing her a song, so my radio suddenly had technical difficulty and I had to turn it off. You could also hear conversations when people were approaching and had radios on the same channel, so that was a nice advanced warning. Mine were supposed to have a beeper that would let you know when a trail groomer was close. The trail groomers in Michigan put out a signal and some radios have the frequency to pick it up. I didn't rely too much on that. All the years I rode with them and I only heard the beeper a couple of times, and I passed a lot of groomers. Get radios with a long distance rating. I'm sure it goes by straight line with no interference. Mine are rated at something like a mile, but going through twisty trails and lots of trees, we were lucky to get a half mile.
Shark