Does exist a way to retrieve SIM telephone number (API or AT cmds) ?
No, there isn’t: because the phone number (MSISDN) is held in the Network - not on the SIM.
Some networks provide a facility to retrieve the phone number; eg, on Vodafone-UK, you dial *#100#
However, many SIMs come preconfigured so that AT+CNUM will give the number.
AT+CNUM just uses the entries in the “ON” phonebook - so you can set it up yourself…