Transition between circuit-switched calls and video calls

A method performed constructed over a first network and an Internet Protocol IP video call over a second network to a client device for the transition between a circuit-switched voice call, wherein the client device includes a camera for capturing video for the video call, the A method comprising: Receiving inputs from a user of the client device that it changes from the established circuit-switched voice call to an IP video call, wherein the built-up circuit-switched voice call a plurality of subscribers, including the user of the client device has, and a number of a or more remote sites in a series of one or more client devices has; Causing transmitted is an IP video call invitation message to the series of one or more other client devices from the set of one or more remote subscribers; Receiving an IP video call acceptance message from the set of one or more other client devices from the set of one or more remote subscribers; Transmitting video that was captured by the camera of the client device, to the set of one or more other client devices of the set of one or more remote subscribers; in response to receipt of at least one video frame from each of the set of one or more other client devices of the set of one or more remote participants transitioning from the circuit-switched voice call on the first network to the IP video call on the second network during the Audio of the circuit switched audio call for subscriber communication is maintained open is set up to the IP video call, wherein maintaining the audio of the circuit switched audio conversation transmitting live audio data to each of the series of one or more other client devices of the series by one or more remote participants over the circuit-switched voice call includes until transitioning is complete to the IP video call.