If T-mobile management had to wear clothing made out of their coverage maps, they would be arrested in many localities for indecent exposure.
No doubt. They haven't actually added many (if any) physical towers to their network. They're relying on their "extended range LTE" bands to give the appearance of additional coverage. Where I have actually witnessed additional Verizon towers being built within the past year to cover the last few remaining gaps, TMO has done nothing. It's a budget gimmick network that really only benefits those in and around major metropolitan areas.