I switched from AT&T to T-Mobile last year and while I agree T-Mobile is a bargain, you get what you pay for. While the coverage is decent where I live (Silicon Valley), indoor coverage is often lacking and rural coverage (e.g., weekend road trips) is often horrible. And their billing system is really third class. Out of about 16 months I have been on T-Mobile, at least half had billing errors.
I strongly suspect that when and if T-Mobile catches up to competitor in terms of coverage, you will be paying substantially more (at least for new customers).
Having said all that, T-Mobile is single handedly responsible for driving down prices (or sweetening the deals) of competitors.
Agreed. Bought unlocked iPhone 6 to use with T-Mobile -- everything about them was good except coverage. Unfortunately, I am rural (south of San Jose) and coverage stinks around my town and I got "no service" as soon as I stepped inside most stores or businesses.
Had great coverage in San Jose and other major cities, but as I travelled I soon ran into the same problem - poor or no coverage in many suburbs and weak or no service inside buildings.
After research I found that the suburb issues can be fixed by T-Mobile building/leasing more towers and placing them closer together, but the building penetration problem is bigger. T-Mobile doesn't have much spectrum in the 700MHz range, most of their bandwidth is the higher frequencies which cannot penetrate buildings. So unless T-Mobile is willing to spend millions/billions to buy more desirable frequency at the next big FCC auction next year (and ATT / Verizon don't outbid them), there is nothing they can do to fix their building coverage problems. As an aside, that is why John Legere has been so vocal about changing the FCC rules and reserving more prime freq for "smaller carriers" but the FCC just struck down his request.
Had to switch to Cricket (MVNO for ATT) to get good coverage.