I always have used a T-Mobile pay-as-you-go plan and have good cell coverage. I buy a $100 pre-paid card for 1000 minutes and it lasts me over 6 months. No data though, but I don't need it. I sit in front of a computer all day and have access to anything I need.
I buy a new unlocked phone every few years. In fact, just bought a BLU Studio Energy 2 last night for $130 on Amazon.
Studio Energy 2