Method for SIM card replacement, aimed to obtain the functionality of a first SIM card storing a real IMSI number associated to a real MSISDN (MSISDNrA,MSISDNrB), the method comprising: providing a user with a replacement SIM card storing a fake IMSI number (IMSIfA,IMSIfB); associating the fake IMSI number (IMSIfA,IMSIfB) with a fake MSISDN (MSISDNfA,MSISDNfB); setting unconditional call forwarding of all incoming calls aimed to the real MSISDN (MSISDNrB) to the fake MSISDN (MSISDNfB); for each call originated from a calling mobile station (1af) using a replacement SIM card, replacing the calling party number (MSISDNfA) with the real MSISDN (MSISDNrA).