A method of controlling a call between first and second user terminals, the method comprising: during the call, detecting a failure of a connection between the first user terminal and a packet-switched network; and in response, causing the call to be conducted at least part way via a PSTN network, via a connection between the first user terminal and the PSTN network. The call may be initiated by the first user terminal (such that the first user terminal is the caller and the second is the callee). The call may be initially conducted, prior to the failure, via a packet-switched connection between the first user terminal and a packet-switched network. The method may be implemented by a client application run on the first user terminal. Alternatively, the method may be implemented by a server.