I've setup a Freeswitch which works when connecting devices directly to it.
But with a Kamailio Dispatcher setup in front, it fails. It reports the error:
2011-09-30 08:47:04.309900 [ERR] sofia_reg.c:2136 Cannot locate any authentication credentials to complete an authentication request for realm '"10.0.1.7"'
I've setup tshark on FreeSwitch now to analyze the input from both scenarios.