Log into the SmartNode via telnet with HyperTerminal, PuTTY, TeraTerm or any other terminal program that supports logging to a file (you will probably also want to switch off line wrapping).
Enable session capturing and then issue the following commands
enable
show running-config
debug context sip-gateway signaling detail 5
debug context sip-gateway error detail 5
debug call-control detail 5
debug call-router detail 5
Make your test call
Wait for the traces to stop outputting
Close the captured file & inspect in your favourite text viewer.