An IMS registration and session initiation is disclosed for a user equipment (UE). The UE has a subscription identifier comprising an IMSI and/or MSISDN. A PDN-GW establishes (s10) an IP-CAN session with a PCRF, for the UE, by transmitting, to the PCRF, the subscription identifier of the UE and an IP address assigned to the UE. The PCRF binds (s20) the subscription identifier to the IP address assigned to the UE for the IP-CAN session. Then, upon the UE initiating the IMS registration, a P-CSCF transfers (s30), to an S-CSCF, an IMPU. The S-CSCF obtains (s40), based on the IMPU, the subscription identifier of the UE from a user database. The S-CSCF transfers (s50) to the P-CSCF the obtained subscription identifier of the UE. The P-CSCF binds (s60) the subscription identifier of the UE to the IMPU. Then, upon the UE initiating an IMS session associated with the IMPU, the P-CSCF establishes (s70) an AF session towards the PCRF with the subscription identifier bound to the IMPU. The PCRF then identifies (s80) the correct IP-CAN session by matching the subscription identifier with the one of the IP-CAN session.