A system, method and computer-readable medium for allowing the use of an alternative numbering plan for delivering short messages to mobile subscribers using the public mobile telephone network is provided. Users of an enterprise or other closed networks as well as users that are not part of a closed network may send short messages destined to members of an enterprise or closed network from their mobile or other devices associated with their subscription using an alternative enterprise directory number, such as the office number, instead of the mobile number, such that the alternative number will be presented at the destination device as the originating number. The recipient may respond to the message by addressing the response to the enterprise or closed network number, and the response may be delivered to the originator's mobile or other device associated with their subscription.