If you're like me and you yell/scream/swear a lot when you're riding, a voice-activated radio will likely annoy everyone else on the frequency.
Personally I'd go with an FRS radio with a lapel mic... most have a connector for one, and you can find 'em on ebay for pretty cheap. Radio shark *might* have them, but every time I've gone there recently i've been quite disappointed. Thing with the FRS rigs is most everyone on the mountain has one.
Motorola makes good radios... don't cheap out when it comes to communication. There's a big performance difference between the $10/pair radios and the $60/pair radios ($30 per radio is still really cheap, considering what one like mine runs for).
Here's my rig... radio gets strapped to my pack, keypad/dial locked. Mic grabs onto the shoulder strap on my pack and the cable goes inside hte strap to the radio. I usually pack one or two 2watt commercial VHF radios as well; just in case a group has to split up. Mic doesn't bump against anything, and it's easy to hear and get to.