The present invention provides a technique where application servers can initiate sessions within the IMS network by initially sending session initiation messages to the I-CSCF. By routing the session initiation messages to the I-CSCF, the application servers need not directly access the HSSs in order to initiate sessions. Upon receiving a session initiation message from an application server, the I-CSCF may access the HSS to identify an S-CSCF to use for session control and then route the session initiation message to that S-CSCF. The S-CSCF may then access the same or different HSS to determine how to further route the session initiation message to establish the session. The session initiation message may be routed toward other S-CSCFs en route to the appropriate user elements. The session may be a session established between user elements or between the application server and a user element.