How much tax would I have to pay on an iphone sent from the US?

I'm looking to buy an iphone 4 from amazon US. It is £105 used compared to the UK where it is £200. How much tax will I have to pay? I think it is only VAT on items under £135 so is it just 20%? Also, if it is locked to an American network (Verizon) will it work on a English network if I get it unlocked here or will I have to jailbrake it?

£105 + vat + collection fee, and locked to foreign network, don't bother.