A tandem switch migration method is provided according to the invention. The tandem switch migration method migrates at least some end users from an old tandem switch of a Public Switched Telephone Network (PSTN) to a new tandem switch using a Local Number Portability (LNP) capability. The method includes configuring a Local Routing Number (LRN) information of the PSTN in order to direct inbound cells from the PSTN through the new tandem switch and to an old node. The method further includes programming routing information of the new tandem switch to direct inbound calls from the PSTN to a new node after at least a portion of end users of the old node have been physically moved from the old node to the new node.