Method and apparatuses for establishing a secure channel between a user terminal and a SIP server

A method of establishing a secure communication channel between a user terminal and a SIP server for the purpose of controlling a service or services provisioned by the SIP server, the method comprising:

• sending from the user terminal to the SIP server a session initiation request, via an IP Multimedia Subsystem network, wherein the IP Multimedia Subsystem network authenticates the user terminal and incorporates a P-Asserted-Identity into the request as a result of the authentication;
• at the SIP server, authorising access to the service on the basis of said P-Asserted-Identity;
• and,
• upon successful authorisation, sending to the user terminal a security token, via the IP Multimedia Subsystem network, wherein the SIP server and the user terminal use said security token to establish a secure communication channel between each other.