Abstract: The basic idea is to enhance functionality of the Signaling Relay Function for support of MNP (MNP-SRF) so that the normal HLR query in the circuit switched domain is bypassed and the call is routed to an IMS domain. The SLRF, upon receipt from a GMSC a SRI message containing the real MSISDN number of the called party, translates the MSISDN number to a new MSISDN number and responds to the query by sending a message containing routing information to the IMS domain and the new MSISDN number. Alternatively, the original MSISDN number is used in the response message but a certain identifier is then added into the message. Then the called subscriber is first tried to reach in the IMS domain where the subscriber is likely residing. In case the subscriber yet resides in the circuit switched domain the call is routed from the IMS domain back to the circuit switched domain and not until then the normal HRL query is performed.