Port Within is defined as the ability of end-users to retain the same telephone number(s) when moving from one service location to another, that is, T&F within a Rate Center.

Port Within can also be noted as moving TNs from one switch to another within the same Central Office. This is often done when moving DID TN(s) from one trunk group to another, when they have been established on different switches. This process may also include a conversion and a move via a single order request, with number port to a new address outside the existing switch, but within the same Rate Center.

Detailed information is described in the
Port Within PCAT