The PLC's serial port must already be cleared of protocol. The modem must be configured to speeds of 9600, no parity and 8 data bits. The local echo of the modem must be disabled with the command ATE0.
The FB takes the phone number from the DM, and sets it as a sequence of ASCII codes and the string of SMS. For both there must be a byte = 0 after the last character.
Within the FB you have to specify the DM which you have taken the phone number from as a constant boundary (eg & 100 -> D100), the same applies to the string of text message.