A user equipment device including a mobile terminal (11b 11b') and a terminal equipment device, said mobile terminal being coupled to said terminal equipment device, for use in multimedia communication requests for internet protocol communications across a packet switched communication network where the multimedia communication requests are made using signaling according to a session initiation protocol, wherein the TE includes a user agent (UA TE) for providing a communication establishment message (INVITE) as part of the signaling and including a session description protocol component, said UE device being characterized by comprising: a) an IMS proxy adjunct (P+), located in the TE device, responsive to the communication establishment message (INVITE) and other messages including the SDP component, for making extensions to the communication establishment message (INVITE) and other messages by extending the SDP component so as to reserve resources ensuring a predetermined quality of service (QoS) for the IP communications, and for originating and terminating messages according to the session initiation protocol on behalf of the user agent (UA TE) in the TE device so that the packet switched communication network need not take into account the operation of the IMS proxy adjunct (P+); and b) an IP router and QoS manager, located in the MT (11b 11b'), responsive to control signals provided by the IMS proxy adjunct (P+), for providing QoS using access network specific procedures to open QoS enabled IP flows, and routing IP packets to different QoS enabled IP flows, wherein the MT is operative according to a procedure for registering with an Internet Protocol Multimedia Subsystem server so as to allow the MT to access, over a digital communication system, an IP multimedia service to which the MT is subscribed, the procedure including having the MT send an SIP register message to a proxy call session control function (P-CSCF), wherein the SIP register message sent according to the procedure includes a field conveying information indicating whether the MT includes IMS proxy functionality. a) an IMS proxy adjunct (P+), located in the TE device, responsive to the communication establishment message (INVITE) and other messages including the SDP component, for making extensions to the communication establishment message (INVITE) and other messages by extending the SDP component so as to reserve resources ensuring a predetermined quality of service (QoS) for the IP communications, and for originating and terminating messages according to the session initiation protocol on behalf of the user agent (UA TE) in the TE device so that the packet switched communication network need not take into account the operation of the IMS proxy adjunct (P+); and b) an IP router and QoS manager, located in the MT (11b 11b'), responsive to control signals provided by the IMS proxy adjunct (P+), for providing QoS using access network specific procedures to open QoS enabled IP flows, and routing IP packets to different QoS enabled IP flows, wherein the MT is operative according to a procedure for registering with an Internet Protocol Multimedia Subsystem server so as to allow the MT to access, over a digital communication system, an IP multimedia service to which the MT is subscribed, the procedure including having the MT send an SIP register message to a proxy call session control function (P-CSCF), wherein the SIP register message sent according to the procedure includes a field conveying information indicating whether the MT includes IMS proxy functionality.