Porting a number to an existing family plan in a different city?

I want to switch carriers but keep my number. I currently have an area code for my dad's city on T-mobile, but I want to switch to AT&T. My mom's family plan is in another city, but in the same state, with a different set of area codes, so would it be possible to switch carriers but keep my original number that has a different city's area code from the other plan members on my mom's account rather than having to open an independent account?