A method including receiving, at a CSCF (Call Session Control Function) portion of a home network in which a mobile station is subscribed, an IMS (IP Multimedia Subsystem) registration request from the mobile station via a visited network to which the mobile station is attached; establishing an SIP (Session Initiation Protocol) session between the mobile station and the CSCF server in response to the received IMS registration request; receiving, at the CSCF server, a SIP INVITE message from the mobile station during the SIP session, wherein the SIP INVITE requests use of a service; obtaining an identifier for the visited network; obtaining, in response to receiving the SIP INVITE message, a first roaming policy based on the identifier for the visited network; determining whether the SIP INVITE message is acceptable based on the obtained first roaming policy and the service requested by the SIP INVITE message; and sending a response for the SIP INVITE message to the mobile station, wherein the response is based on the determination whether the SIP INVITE message is acceptable.