I'm a total noob. Will flashing an AT&T phone with a tmobile rom allow wifi calling?

I recently got a hand me down phone from someone who had AT&T phone. It's an i747, but I unlocked and use it on the Tmobile network now. In Kansas City, about a week after I activated service, they disable some of the frequencies that my phone uses, apparently. I get data and texting relatively fine, but I can't make or receive calls most of the time. The settings don't allow me to activate WiFi calling, I assume because AT&T decided to disable the option, because they don't support it. If I flash my phone with a Tmobile rom, will it allow me to activate that setting, and make/receive calls over the 4g/LTE connection?

Thanks.