A method, application server, and Serving Call/Session Control Function (S-CSCF) for allocating a SIP Application Server to a subscriber in an IP Multimedia Subsystem. A Home Subscriber Server (HSS) identifies for the subscriber, a set of provisioned initial filter criteria, which contains at least one generic SIP Application Server identity. The HSS sends the filter criteria to an S-CSCF allocated to the subscriber. The S-CSCF resolves the generic SIP Application Server identity into a plurality of application server addresses, with one of the addresses being allocated to the subscriber for use in provisioning a service to the subscriber. The S-CSCF caches the address allocated to the subscriber for subsequent use.