If you received an ABC Voucher letter and T-Mobile is listed as one of the providers in your letter, then you should have good enough coverage to meet the program requirements. You see we knew this would come up and we got ahead of it! The state and T-Mobile got together and compared notes to figure out who would get good enough coverage and who wouldn't. The letters are only supposed to go to the families in areas of good coverage. And that is in more places than ever these days. They have built more and more towers and are utilizing technology to make those cell signals travel further and cover more families. And the work continues!
If you want to check it out for yourself, T-Mobile has a great tool where you can put in your address and it will give you an idea of what 4G LTE coverage will be at that address, You find that tool HERE.