you can use AT+CRSM command to read file EF_MSISDN (MSISDN) from the SIM.

EF_MSISDN : Identifier: ‘6F40’ = '28480’dec
This EF contains MSISDN(s) related to the subscriber.

e.g.:
AT+CRSM=176,28480,0,0,14
+CRSM: 144,0,“0791942143658709FFFFFFFF”

Where '07 is lenght and ‘91’ is coding.
Number starts at byte 3 and the values is LSB first…means, each byte needs to be turned:
‘94 21 43 65 87 09’ wents to be:
49 12 34 56 78 90 -> +491234567890