In the olden days, if your cell number had a different area code from the place you were physically in, you'd get long-distance charges when calling a local number, but not when calling a number matching your area code.

In modern times however, the area code is largely irrelevant. You get assigned a number with the area code of the place you first opened your account, and then you can just keep that number forever if you want. I've had the same number for almost 20 years and I've had four different providers in that time. Porting a number between carriers has been a standardized process for a very long time.