Vodafone offers 24-, 18- and 12-month contracts. You can pick up the handset for free on a 24-month, £45 per month contract. If you are after something shorter and cheaper, you can get a 12-month, £35 per month deal, though you'll have to stump up £299 up front.

O2's tariffs start from £21.50 per month on a 24 month contract with 100 minutes, 500 texts, 20MMS, and 500MB of data, and an upfront cost of £304.99. O2 also includes tethering as standard. However, you can only buy the white iPhone 4 in O2 stores and not online.

Three is offering 24 month contracts from £25 a month or on The One Plan for £35 a month, including unlimited data, 2,000 any network minutes, 5,000 minutes to other Three handsets and 5,000 texts. There are also pay-as-you-go plans.

More: http://www.computerworld.com/s/article/9216244/