The way I remember it in the US was in the 3G age you had good cell service in cities like Rochester, NY which have moderate populations and gentle hills but it was spotty in dense cities with crazy geography and/or urban canyons. [1] Like I used to stay at a motel two blocks from Hollywood and Vine and my phone barely worked. Once 4G was rolled out, coverage got good in Nielsen "A" markets.

[1] ... and there was that summer my son and I tried to visit as many state parks in upstate NY as we could and I had phones on both the AT&T and Verizon networks that had terrible coverage away from certain big roads.