This is excellent news!
The BT Voyager 2000 router was at fault. Getting a different code release installed on the BT router permits port 5060/SIP traffic.
It appeared to be blocking at the network level because the BT router was not showing the traffic as being blocked, as though it never got to the router. It was not a misconfiguration, just a (very nasty/ugly) bug in the BT router code.
my comment like many i know is the BT2700HGV i was supplyed by them for 3 weeks i had no problems using this already configured router to acess irc, then its come that everyone on bt is having trouble acesessing files they send or recieve and when i check the logs in my firewall it shows as the ports are in fact blocking the send/gets. ive contacted bt along with many others only to have them say theres no problem. now bt have said to some customers there is a ptoblem with certain ports and the rest like me have been told theres no blocking of any ports. ive removed my router and pluged in my modem with i used for around a year with bt prior and theres the same problem. the files dont send or recive. anyone got any ideas?