Howdy,
I've been playing around with this SIP scenario tool. Maybe I'm just the last one to find out. But after ngrep'ing one too many packets this is really refreshing. It is a freeware application and it's output is either html or text. I've uploaded a couple of files to my website so you can see the call flow diagram capabilities.
The source (perl) code can be had at: http://www1.cs.columbia.edu/sip/implementations.html under sip scenario.
The example (real world debug) callflow can be viewed at my development website: http://stage.august.net/sip1_index.html and http://stage.august.net/sip1.html
You use tcpdump (or ethereal, or whatever) to grab the Output, like on linux: tcpdump -s 0 -i eth0 'port 5060' -w /var/log/sip1.dump
It has been kinda quiet on these lists.
---greg