Thanks all for the help and pointers everyone.
Suprisingly enjoyable and "dh" in the rules file does a ton of work for you!
I've emailed the VoIP packaging group to see if I can help now that I know some more. I'd like to look after the libosip2 package too as SentryPeer requires it and it looks like it's not been updated in 6 years?
Thanks again everyone.
Gavin.