I found this piece interesting as, to be honest, I have had experience with this myself first hand when my wife visited family in Montana. Long story short: Never use an AT&T phone in Montana. Short of a very select number of bigger cities, you will find yourself reaching for the Verizon phone every time.
Now here is where things get interesting. States like Washington, among others, are clearly iPhone using states. More rural areas, on the other hand, largely appear to be Android using areas. The clear exception appears to be Alaska, which is interesting. But considering the population centers mostly being in the southern part of the state, maybe this is why.
But the undeniable fact that coverage is apparently having a major play on who is using what mobile phone is fascinating to me. What is going to be even more interesting is when we see the iPhone moving onto other networks. That could become a real game changer by itself.