how does it work? I'm on vodafone, and travelling to USA, and I think the network for me over there is 'rogers' - will the N900 know that rogers is a foreign network??[/QUOTE]

Rogers is actually only in Canada. i believe the only US network that will give you full 3.5G speeds is T-Mobile. This all depends on the roaming agreements set up by Vodafone, and yes your phone will know you are roaming.