I just found this post after searching for "ip phone" & "virgin media".
I have had a working IP Phone at home for around 2 years, up until an internet outage a few weeks ago. We lost the internet for over 4 hours, and it was a local network/cable issue.
After service was restored my working IP Phone stopped working - it stopped being able to register with my firms tftp server. To cut a long story short I tried 2 ip phones (cisco 7965) with no luck, this morning went into the office and got my phone working on the guest vlan (ie 'external' to the firms network). I brought it home this eve, and when I plug it in it cannot register still.
I KNOW the phone works. It USED to work at home on virgin media (cable modem, connected via ethernet, not superhub), but since that outage it no longer works.
Aside from rebooting it, no other changes were made to my cable modem.
Have VM changed something on their firewalls which is preventing ip phone traffic I wonder?