I was on the Vodafone eForums yesterday and people have been asking about flashing their N900's to the UK/Global firmware and whether that will invalidate the warranty. A Vodafone representative said that if the firmware downloaded is from a nokia approved site (any subdomain on nokia.com for example) and the phone is flashed with a Nokia approved flashing tool (again, like the ones available on the Nokia website) then debranding your phone will not void the warranty.

So my N900 is now on Global firmware, which I assume is unlocked (nothing but Vodafone sims in this house, so I have no way of knowing) and because it's on the Global firmware, it's generic too.

EDIT: http://forum.vodafone.co.uk/index.ph...ic=53991&st=20 Here's the thread I was looking at, look for posts by "MartinB_Vodafone" in particular. He says there that any firmware available on the Nokia website will not invalidate the warranty.