Provided is a method for initiating a mobile voice call from a caller UE to a callee UE having a SIM card associated with a callee phone number, which callee phone number is a E.164 compliant MSISDN. The method includes providing a software function at the callee UE, which software function is associated with a receiving address comprising the callee phone number, and configuring a call forwarding function in a first network, being activated for the callee phone number and configured for forwarding CS voice calls to a forwarding phone number associated with a VOIP service. The method also includes the caller UE calling the callee phone number, the first network performing the call forwarding to the VOIP service, the VOIP service identifying the callee UE, and the VOIP service initiating the call between the caller UE and the software function using the receiving address.