Update: I returned it to the service centre last week. They rang yesterday; flashing it failed to fix the issue apparently (... ) so they've sent me back the brick and told me they'll ring if there's a software update that might help.

To be fair, the N900 was never released in NZ, and it sounded like they may have been a bit out of their depth, but brings a whole new meaning to service; You send us a brick, we can fix it to work like... a brick. Does buying over the internet void your warranty?