Good news as I expected the answer to be a flat "No".
Two further questions:
Presumably then there is an access code or feature key to access that trunk when you want to make a Skype call, or would all calls default to Skype?
How easy is this to set up? Our Vendor is also our local telephone service provider and they are not going to be too keen, or in fact may well flatly refuse to setup this arrangement.
Thanks for all your help.