I am sure I have read somewhere that other people have added W'n'W to this and you can cancel at any time - if you move to another Tarrif you would not be a new customer if you kept the number - presumebly you could take another number and port the number out and back in again if you really wanted too but it is something to bear in mind.
I'm going to check this out and see if I can put the pro data package on it. Then I will try and unlock my Voda 3G PCMCIA card to give my unlimited laptop data on the move. I will also use it to check out the Orb client properly on my phone. Sweeeetttttt. I'll let you know if I get a reply.