A method of distributing application server addresses in an IP Multimedia Subsystem. Upon allocation of an application server to a subscriber, the allocated or another application server sends at least one application server address to a Home Subscriber Server (HSS). The HSS stores the address(es) in association with the subscriber identity and sends the address(es) to a Serving Call/Session State Control Function (S-CSCF) allocated to the subscriber. The S-CSCF caches the address(es) in association with the subscriber identity and uses the address(es) to send subscriber-related messages to the allocated application server.