Help! Sprint TP2 sim unlocked on Tmobile

[NIKKG]

I have a question about tmobile service on a sim unlocked Sprint TP2. A few days ago, I gave my GF a Sprint TP2 after I paid to get the sim unlocked. Anyways, tmobile worked, but in certain areas like near her work, she couldn’t get service, so no calls or texts whatsoever, but when she gets home the tmobile service is working again.

Is there a reason she might have no service in some areas? I setup the phone to only use GSM service and I did manual settings and selected Tmobile. Do you guys think maybe tmobile might have a different voice band in different locations that the Sprint TP2 can’t pick up and that’s the reason she gets no service? She only wants the phone for talk and text and doesn’t need the data.