A method for an access network node, and the access network node, to provide a user device access to a service enabled by an IMS network, comprising the steps of: setting up an IP tunnel for communication with the user device, sending an authentication request to the user device via the tunnel, receiving a response to the authentication request from the user device via the tunnel, authenticating the user device, sending a registration request comprising an IMPU associated with the user device to an IMS network node, receiving a confirmation message from the IMS network node that the user device is authenticated, sending an authorization confirmation message via the IP tunnel that the user device is authorized, receiving a service request via the IP tunnel from the user device to start the service, sending a service session initiation message to an application server associated with the service.