A telecommunication system comprising at least one server running a computer program which enables said server to: - receive a request from a calling external telecommunication device for a telecommunication connection with a receiving external telecommunication device; - establish a data connection with said calling external telecommunication device in response to said request; - receive from said calling external telecommunication device a receiver identifier and store said receiver identifier; - establish a data connection with said receiving external telecommunication device using said receiver identifier; - transmit to said receiving external telecommunication device, after a data connection with said receiving external telecommunication device is established, a server identifier, characterized in that said computer program further enables said server to - close said data connection with said receiving external telecommunication device after said transmission of said server identifier; - receive a request for a telecommunication connection from said receiving external telecommunication device via said server identifier within a time slot after said closing; - check, in response to said request for a telecommunication connection from said receiving external telecommunication device via said server identifier, if a receiver identifier of said receiving external communication device matches said stored receiver identifier, and - establish a telecommunication connection through said server between said calling external telecommunication device and said receiving external telecommunication device if the receiver identifier matches said stored receiver identifier. - receive a request from a calling external telecommunication device for a telecommunication connection with a receiving external telecommunication device; - establish a data connection with said calling external telecommunication device in response to said request; - receive from said calling external telecommunication device a receiver identifier and store said receiver identifier; - establish a data connection with said receiving external telecommunication device using said receiver identifier; - transmit to said receiving external telecommunication device, after a data connection with said receiving external telecommunication device is established, a server identifier, characterized in that said computer program further enables said server to - close said data connection with said receiving external telecommunication device after said transmission of said server identifier; - receive a request for a telecommunication connection from said receiving external telecommunication device via said server identifier within a time slot after said closing; - check, in response to said request for a telecommunication connection from said receiving external telecommunication device via said server identifier, if a receiver identifier of said receiving external communication device matches said stored receiver identifier, and - establish a telecommunication connection through said server between said calling external telecommunication device and said receiving external telecommunication device if the receiver identifier matches said stored receiver identifier.