Having just returned from a trip across the pond -
I would advise the N800 + an unlocked cell.

Where you can buy a pay as you go sim in most countrys,
the earlier comment about having a permanent address applies.
I also found that some needed to fill out papers and give them passport
type photos (like I did when in India).

Another option is a world sim card (I use this one -
http://www.mobalrental.com/gsm/sim.asp).

Where as the minute rates are not wonderful - it will work in a pinch
anywhere (Ive used it in Ireland/UK/France/Italy/India/Mexico/the carribean) - and there is no contract fee. Just give them a credit
card for billing/shipping, pop the sim in an go. I got mine in about 3 days. It is a UK phone #.

Pay as you go rates in Ireland/UK back to the US were about 1euro
a min - about the same as the mobal sim. So I didnt do it.

In India the local pay as you go rates the the US were almost skype rates...

If you want to try mobal - let me know, as they have a refer
a friend program and it will give you some additional free $$.

Another thought is to enable Boingo on your N800. The have a
pretty good plan ($8month) and then you can access the local
pay wifi networks without having to find an unlocked wifi site.

Ed