Anyway, thanks to the wonders of Norlog I’ve got hold of a document that helps you to make sure that if you want to use the Satellite Navigation you won’t get hit by heavy roaming charges. It describes how to set up the phone so it won’t download maps willy-nilly (fine on T-Mobile’s excellent Web n Walk tariffs though) and how to get the maps in other ways.

Nokia N95 Basics - pdf file

Thanks go to Rich. Unless asked by him I won’t put any more info in case it gets anyone into trouble.