A user with a terminal residing in a Circuit Switched (CS) telecommunication network calls a party having a terminal residing at a Packet Switched (PS) telecommunication network, the CS and PS networks connected to each other by gateway entity. The party to be called at the PS network is addressed by means of a Session Initiation Protocol Universal Resource Identifier (SIP-URI). The call setup is performed in a two step process. In a first step, the terminal sends a the SIP-URI in a message together with the address of this terminal to a network entity which stores said message. In a second step, the terminal calls the network entity, wherein the network entity selects the stored SIP-URI and resolves the SIP-URI into an address of the terminal at the PS network and instructs the gateway entity to connect the calling terminal to the terminal.