I've spent the last day trying to configure the trunks on my new SnomOne SOHO. This morning I tried using the IP address instead of the FQDN and now everything works.
Checking through the logs it seems the Snom was looking for the DNS at 127.0.0.1 (ie on the local device). There doesn't appear to be a way to force a change of name server.
In short - everything is OK IF I use the IP address (BTW I've checked with 3 different VOIP providers) - but this isn't a proper fix as I don't know how often the IP address is likely to change.
Also - as a consequence of the above I can't update the software using the autolink as the web address is not recognised by the Name Server.
Help appreciated.