Cell phones: T-Mobile

California Reception for T-mobile

I don't know about the rest of the west coast, but here in SF to LA, T-Mobile receptionin is pretty decent. It's generally known that if you are near a major metropolitan area, you can get good to excellent reception. The more you get into rural areas, the more 'spotty' it would get.
My daughter had a T-mobile SideKick 3, and she never complains about not having reception here in the SF Bay Area. Naturally, reception (on any cell arrier) would be diminished when you walk into a thick concreted building, but me, nor my duaghter, experienced dropped calls.
With that said, of course there are 'dead spots', but that's with any carrier...just at different places. I've used all major cell carriers(Sprint, ATT/Cingular, Tmobile, and Verizon).

Hope that this helps and good luck.