Portable -- as in that tel. number follows when you go to another carrier. That means you keep your original telephone number. I moved from Albany NY (having an area code of 518) but I live in Sarasota FL, so the area code and/or the local exchange no longer have any geographical relevance as a way of pinpointing my location. It's simply where that telephone phone number originally was obtained from.
Cell phones use towers not landlines and as such are not tied to any home-base geography.