When the controller receives an SMS, the number is stored in an SI vector:
SI 188 Last received SMS number, number of digits
SI 189 Last received SMS number, '+' sign
SI 190 Last received SMS number, 1st group of 4 digits
SI 191 Last received SMS number, 2nd group of 4 digits
SI 192 Last received SMS number, 3rd group of 4 digits
Note that the vector is overwritten each time the controller receives an SMS.
The M90 series does not support this feature. It is supported by M91 and Jazz.