Swap motherboard to unlock/change carriers

So I have an AT&T Samsung Galaxy S5 which is updated to the point that it cannot be rooted. All I want is to be able to use Google Hangouts on this phone to receive/make phone calls. AT&T disabled the phone call feature but allows the texting feature.

I read online if I root the phone I could just change the config that disabled the calling from a 1 to a 0 and it would enable calls, however, my phone is updated too far to be jail broken.

So as a PC technician I was thinking maybe I could just replace the motherboard to a different carrier that allows such things and flash it and perhaps I could get what I'm seeking but I figured before I bought the $100 board I would ask the community.

I know you can do this with iPhones but I couldn't find anything with Galaxy or even androids.