Systems and methods are disclosed for notifying external message centers when a mobile device becomes available to receive a text message. One embodiment includes a message waiting system that identifies a failed delivery attempt of a text message to a mobile device that is unavailable, where the text message originated from an external message center. The system identifies routing information for the external message center based on the failed delivery attempt, generates a Message Waiting Indicator (MWI) record for the text message that includes the routing information for the external message center, and stores the MWI record. When the system identifies that the mobile device becomes available, the system identifies the MWI record that includes information on the failed delivery attempt to the mobile device, and sends a notification indicating that the mobile device is available to the external message center based on the routing information in the MWI record.