The best way to get started using the SIP tasks, is to start by loading any of the example PLC files, found in the extensions/test/sip directory.
The example PLC files are configured by a setting variables using a SetVariableTask at the top of each scenario. Modify as appropriate.
To test simple REGISTER requests, load sip-register.plc.
To test a basic call, i.e create a session between two user agents, load sip-basic-call.plc.
Note the usage of the "Call" parameter to separate each side within the scenario. Also note that by default the local IP address and port is not defined and automatically initiated by SipInitTask. SipInitTask defines two valiables "sip-local-ip" and "sip-local-port" which are used to define contact addresses in the "Init URI variables" task.
You will find a few more examples in the extensions/test/sip directory. Please look at these and contact firstname.lastname@example.org for more examples or questions.