Actually I don't think I ever did get the template to work but I did manage to get it working via the CLI.
It was a fair while ago and I stopped using it when I got a proper SIP phone instead.
http://beusergroup.co.uk/technotes/index.php?title=Voip
Worked on a 6.2.x firmware but as the page says I can't remember exactly where it came from, I think it was probably speedtouchforum.de