Thanks Brian, I'd appreciate you looking - I don't know what to look for in
the sip traces (could be worth documenting some pointers in the wiki?)

The sip trace is here:
http://pastebin.freeswitch.org/16136

I pressed enter a few times in the console before and after it connected to
the extension, so about lines 490-600 is the relevant part.

I also captured a pcap, in case that is of interest - let me know and I'll
email it directly.

Thanks,
Fraser