I found reasonable cell coverage from the summits for Challenger and Triumph, although in both cases I had to force the phone to analog mode (Verizon). ;-)
Now that I've changed to ATT, I find coverage in general to be far inferior to Verizon and in areas other than the I5/I90 corridors it's pretty much worthless. I second Josh's advice - the b/c is no place for an iPhone or similar phones. If you must get an ATT iPhone, also get a cheapo off of Craigslist and pop the SIM card in it before you head out.