thank you all,
so seems like if I want cheap unlimited internet on the go with the N900 in Central and North London to use for Skype A LOT, I'm best off buying the device alone and then going with 3!
or am I mistaken?
(sorry for the "I'm stupid attitude". where I come from, if you're lucky to have a cellphone, there's only limited provideres, all on 2G structures and only 2 tarrif plans exist. So I have to duble check to see if I've understood everything)