Abstract: 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 base

Abstract: A home network may track data usage in real time by a wireless mobile communication device while roaming in a GSM network that is separate from the home network. A Home Location Register (HLR) may receive location information indicative of the location of the wireless mobile communication device in the GSM network. An Online Charging System (OCS) may receive the location information directly or indirectly from the Home Location Register. The Online Charging System may use this location information to determine data rates and cutoff limits which are consistent with subscriber plans and are based on the location of the mobile communication device. This information may be communicated to roaming subscribers in real time and/or used to cut off data communication.