First thing then - I am asking my carrier (Orange) if the 8310 device's PIN is registered to the Blackberry server. We shall see what they come back with. I shall report back to the Forum.
In the meantime, I am not against looking at a more permanent (code) unlock solution... is there a URL or email address for doing what you describe in your post? I would have preferred a code initially to be honest, but most sites on the web seemed to infer that it could take over a working week.