SMS （Short Messaging Services） is the communications mode used to transmit text messages for cell phones and eventually wire line phones as well （see the separate application note， 73M2901CE SMS and Half Duplex V.23 Operation）。 The V.23 half duplex mode has been included with the addition of the B10 command （ATB10）。 The B10 command allows the used to turn the transmitter on and off using the serial interface RTS signal. In this way the modems can easily communicate in half duplex mode using RTS to enable the transmit and CTS to indicate the modem is ready to send data. The V.23 receiver response time has also been improved to allow for fast line turnaround （reversal of the data flow）。 The pattern generator has also been modified to send the proper alternating pattern used in the SMS handshake. SMS messaging is very similar to the format used for Caller ID， so the 2901CE can also be used to send Caller ID messages to equipment designed to use and display Caller ID information. A typical command line for a dial up connection would be： ATY0B10S73-32C2R2S10=255. These commands are broken out as follows：