I have never had a problem using my cellphone anywhere but then I have Verizon as my carrier. I also have onstar in SUV. A lot of vehicles come equipped with onstar so that is handy to have.
I guess its the towers that have issues more than the phones? I just have a track phone, I like that I don't get a bill, and I don't use it that much. I have onstar also, but need to read the manual on how to use it, gld to hear it's reliable for you.