A phone number only messaging experience is provided in an Inter-Carrier Short Messaging System (IC-SMS) service. Subscriber to subscriber messages are routed between carrier's networks using an Inter-Carrier messaging module with appropriate MIN/carrier/carrier routing look-up capabilities. Short messages may be sent to a subscriber in another carrier's network addressed only with a phone number. If the recipient is outside of the sender's carrier network, the Inter-Carrier messaging module of the Inter-Carrier service provider (ICSP) determines the appropriate carrier for the recipient, appends the appropriate syntax to the short message to allow internet protocol (IP) or other standardized communication techniques between SMSCs of the two carriers, and routes the short message to the destination carrier. The recipient in the other carrier's network may reply back to the ICSP's sender using only the subscriber's directory number.