Cell phones are basically two way radios
: The FCC has been rumoring that it is going to take away some frequencies from the HAM radio service and make those freqeuencies available for cell phones. Whether or not that will happen I don't know.
I think cell phones are really hard to use on the mountain becuase the buttons are so small. Another strike against them is they are not nearly as robust as the radios I use. As far as reception goes, it depends entirely on your location. I get lousy reception in the middle of Dallas sometimes.
I have never skied in really cold weather, but my radios have worked all the way down to 5* F with no problem. Just keep them in a pocket and they should stay warm enough.