A mechanism for providing a connection from an IP-based network to a circuit-switched network, such as a GSM network is disclosed. A temporary routing number for the circuit-switched network, such as an E.164 number, is delivered to a user terminal, and a circuit-switched call leg is established from the user terminal to the IP-based network using the routing number. Thereby, IMS-services are provided for end users which are located in the radio access network not having sufficient QoS required for voice over IP. In the example of a conference call service, a request for a conference call may forwarded via a data channel or data path to an application server which provides that conference call service. The application server then selects a conference routing number and returns the routing number to the conference host terminal via the data channel. Using the received conference routing number, the conference host terminal can then set up a circuit-switched connection as a call leg of the conference call.