Right now it would be no service with the exception of 911 as long as any carrier has coverage there. Any cell phone can dial 911 on any provider since that is legal requirement.
It does look like T-Mobile has acquired 700 A Block spectrum (low band) which carries farther and penetrates better so is much more suitable for more rural areas since 1 700 tower can cover 4 higher band towers. Even though T-Mobile acquired the spectrum over 3 years ago that area had a restriction that prevented T-Mobile from implementing it because the was a channel 51 operating in the area and there is a chance of interference. T-Mobile made an agreement ($$) with the channel 51 to relocate to free that channel but it is a process to get the FCC to approve the move and then for the station to change their transmitter. That was finally approved beginning of the 4th quarter last year so T-Mobile can start working on it. Of course they can't do the entire country at once and in a lot of areas where they already have a presence it goes faster because they already have infrastructure (tower, data lines, etc). Where as here it looks like a mish mash of their own towers, partner towers and nothing so who knows what kind of time frame that is. For all we know they already are but they don't say what areas they are working on, my guess is to keep their competitors in the dark and frankly their competitors do the same thing.