For anyone in the market for the an iphone 4 the website topcashback* promises £100 back for contracts taken through e2save. This works for Orange, TMobile, Vodafone and O2 but unfortunately not for Three who currently have the cheapest iphone 4 deal (yes I know officially Tesco have a cheaper one but finding one seems to be as difficult as locating the pot of gold at the end of the rainbow!).
Moneysavingexpert have a great comparison of the iphone deals here
Personally I really want one, but like the government I am going through my own personal deficit reduction so taking on a new contract is out for the time being.
NB this is a referral link which means I get a kickback if you sign upto the topcashback site.