Is SMS data 8 bits until transmitted? <p>A lot of what I have recently read about SMS uses a specification of 140 octet characters, where most uses of SMS I am aware of use 160 septet characters. A UDH is 5 octets long, meaning if I want to send concatenated SMS I would only have 135 octet characters for my message data. This would allow me 154 septet characters after the UDH. </p> <p>Do I take a 154 octet character message, append it to the 5 octet UDH, and send this to the modem as the message text, or do I have to encode my 154 message octet characters into a 7 bit character string, encode the UDH as a 7 bit string, concatenate the two, and send that text to the modem?</p>