After dropping out of the IRC channel I thought my 403 - Forbidden was possibly a NAT issue, so I unhooked my modem.
Turns out:
Firstly: I had the wrong password (must be cos it was after midnight)
Secondly: With the correct password, it was looping (i had sip_trace set to on). I changed the port number in x-lite (softphone used for testing) to 5070 and then it was no dramas - it worked.
Thanks to the people on #freenode for helping me out on my first steps to mass scalability!
Chris - (zirtron)