There are many radios in use, but obviously ones that do not need a licence are common and nice.
In North America, there are a radios commonly referred to as FRS radios. These work within the Family Radio Service frequency band (462MHz), most of which can communicate with each other.
In Europe, most countries allow the use of the PMR band (446MHz).
| Note that it is illegal in North America to use the European PMR radios, and it is illegal in most (if not all) of Europe to use the American FRS radios. |
In either continent, these types of radios are limited in their range, and can be dramatically affected by terrain. It's unlikely that you'll talk to someone on the other side of the mountain, but the other side of the valley is possible. That said, there have been reports of suprisingly good and bad results.
It could be said that Motorola are the current marker leaders with their TalkAbout range. These radios have "interference" codes to reduce the chances of meeting someone on the same channel, but if your radio doesn't have them, then you'll hear everyone - including people that do. There is more information on CTCSS if you are interested. Thanks to Steve D for the useful insight into this.
Phones
An alternative is the use of mobile (cell) phones. These have the advantage of obviously having as much range as you like, providing that you yourself are in range of a repeater. As the costs come down and more repeaters are added in the mountains, their use has become more prolific (for better or worse). However the cost of calls can be still be high, especially if you are not in your native country and are suffering the roaming charges. It might be a good idea to put the number of the local ski patrol into the address book or speed dial - however, you should not rely on your phone to get you out of trouble. The cold eats batteries, and you may not get a signal. Don't venture off piste thinking you'll be OK, just because you have your phone!