A system includes a terminal, a wireless access network, an IP telephony network, a core network gateway from the IP telephony network to the public mobile phone network and a network device, which connects the wireless access network to the IP telephony network and adapts the IP telephony network services to be used by utilizing the circuit-switched signaling protocols of the terminal. A location updating request is received from the terminal over the wireless access network. Location updating is performed via a core network gateway. The network device performs user registration to the IP telephony network using a domain name formed by the phone number of the user and the domain name of the network device or the numeric IP address as the address connection to be registered and as location data in the IP telephony network.