Thank you once again for responding so quickly!
in answer to your questions..
Yes, I had set the extention as remote when trying it without the VPN and local when trying it with.
I wondered when that "external ip" in globals came into play, but how would i configure it? apart from entering the panel and filling the box!!

At the HO the path looks a bit like this..
WWW -> wired router -> SME/SAIL -> switch and wifi AP -> LAN
We have had to use what we could find as much as poss due to next to no budget - the server was the only pre-approved new purchase.
We have the ADSL coming in with a dynamic IP, calling around their current and other ISP's for a fixed IP account turned out to be beyond their budget (although I think they are tied into a contract with the current one but that's by the by)
I have got around this using the DYNDNS which is handled by the router and passes a fixed local IP tot the WAN interface of the SME.
I would Guess I put the static lan IP in the globals IP - am I correct in that assumption?
Next - I used SJ Softphone because it was the first supported one I came across i could find a download for - no other reason. I can move over to IAXlite with no problems
I realy appreciate your support in this setup, as a comparison another client of mine has been waiting nearly 2 weeks for an answer from the "Support Department" of a "major" software house that actualy contains usefull info, instead of "we aknowledge your reply........" so thank you again.
I will try these corrections to this setup and report back