Methods and apparatus for routing off-net Short Message Service (SMS) messages between a first service provider network and a terminating service provider network are provided herein. In some embodiments, the method includes receiving a first SMS message including a first identifier associated with a first subscriber of the first service provider network stored in a source address field directed to a second identifier, determining that the second identifier is associated with a second subscriber of the terminating service provider network, associating the first identifier with a local reply identifier in a mapping database, replacing the first identifier in the source address field with the local reply identifier, and routing the first SMS message including the local reply identifier stored in the source address field to the second identifier.