US Patent 8000729 Mobile to mobile text messaging using keyed modulation

A text messaging system conveys text messages between a sender and a recipient in a wireless carrier network. A sender mobile handset includes manual input for identifying text characters in a message to be sent to the recipient and an audio-band encoder coupled to the manual input for representing the text characters with a keyed modulation stream. The keyed modulation stream is transmitted over a non-signaling channel of the wireless carrier network to a base station. At least one mobile switching center in the wireless carrier network transports the message between the sender mobile handset and the recipient mobile handset. A demodulator operating on behalf of the recipient converts the keyed modulation stream to decoded text. A recipient mobile handset including a display interface and a display receives the decoded text and displays the text characters of the message to the recipient.