A method of debugging a telephone call can include, using Session Initiation Protocol (SIP) formatted messages, initiating a debug session between a debugger and a call server for a telephone call established over at least a portion of a packet-switched network. A debug function can be invoked within the call server as specified by a SIP formatted message originating from the debugger. The method further can include determining fault information pertaining to the telephone call using the debug function and sending a SIP formatted response from the call server to the debugger.