The invention relates to a method for causing a communication link to be established between a mobile communication terminal of a mobile radio network and a partner communication terminal of a communication network operating in accordance with the Internet Protocol. The mobile communication terminal is associated with a directory number of the mobile radio network and the partner communication terminal is associated with an IP address of the communication network. To cause a communication to be established between the mobile communication terminal and the partner communication terminal, a text message, sent out by the mobile communication terminal and containing the IP address, is received by a service node connected to the mobile radio network, and the service node sends a task message including the directory number and the IP address to the communication network. Thereupon, the communication link KV is established between the mobile communication terminal and the partner communication terminal.