Calling an Unready Terminal

A user terminal for establishing a VoIP call between a caller and a callee based on a call flow comprising a call establishment request and a corresponding call acceptance response, the user terminal being a terminal of the caller and comprising:

• a transceiver for conducting the VoIP call over a packet-switched network;
• and
• a calling engine arranged to send a first call establishment request to an instant messaging client on a called terminal that is not installed with a VoIP client and therefore unready to accept the VoIP call upon receiving said first call establishment request, the called terminal being a user terminal of the callee;
• wherein the calling engine is configured to generate the first call establishment request in a form that invokes the instant messaging client to download and install a VoIP client on the called terminal, and wherein once the called terminal is thus ready to accept the call, the calling engine receives back from the VoIP client on the called terminal a reverse call establishment request for said call instead of the call acceptance response;
• and
• wherein the calling engine is configured to automatically accept the reverse call establishment request on behalf of the caller, by sending the call acceptance response to called terminal, on condition that the reverse call establishment request was received back from the called terminal within a predetermined time limit.