Methods and apparatuses, including computer program products, are described for identifying an application server in a plurality of application servers associated with a shared identifier in an Internet Protocol Multimedia Subsystem (IMS) network. The method includes receiving, from a Signaling System 7 (SS7) network, a message including a mobile device identifier associated with a mobile device connected to the IMS network and determining the identity of an application server in the plurality of application servers associated with the shared identifier. The determining step includes extracting the mobile device identifier from the message and retrieving, from a data storage module, an application server identifier associated with an application server based on the extracted mobile device identifier. The application server associated with the retrieved identifier provides service to the mobile device. The method also includes transmitting the message to the application server associated with the retrieved identifier.