A system and method for sending SMS messages between wireless communications networks. SMS messages are sent to a hardware device in the originating wireless network, which then forwards the message to a management server via the Internet. The management server forwards the message to the appropriate device in the receiving wireless network, which then sends the message to the intended recipient. Replies can then be sent to the originator of the message. Users can also send messages from a computer to a cellular telephone and receive messages sent from a cellular telephone on a computer via email or an HTML based interface. The system can also be used to send and receive messages from a wireless carrier's SMSC.