Really? My tiny ILEC says our numbers are portable to wireless, but there are no prefixes in their rate centers but theirs.
I was under the impression that you really only need to be present in the LATA, not in the rate center, for portability to work. You just need to be able to provide a routing number for the portability database and as far as I can tell the routing number need not be in the same rate center as the original number. There's certainly no technical reason it has to be.
Inbound calls will still be rated as calls to the original rate center, but cellular and VoIP carriers don't care.