O2 has gone official with its iPhone 4 prices and if you were hoping for the network to seriously undercut the prices announced by Orange, then you're going to be a bit disappointed, because it's all a bit much of a muchness.
Where it differs slightly is that O2 offer a cheaper monthly deal of £25 on a 24-month contract or £30 on an-18 month contract but you'll only get 100 minutes of calls for this and the device will cost you between £209 and £323 depending on whether you take the 16GB or 32GB version and the length of time you sign up for.
You can also get the device for free for a slightly cheaper monthly deal. For £60 a month on the 2 year deal (an extra £5 if you only want to sign up for 18 months) you can get the 16GB version for nowt. For this you get unlimited calls and texts and a Gig of data. On Orange you need to pay £75 a month for something similar.
Otherwise prices are on a par with Orange's albeit with the odd tenner extra on a few packages.
With O2 though, the amount of data differs depending on what deal you take. It ranges from 500MB to 1GB, so bear in mind how much 3G browsing you might be doing. There's unlimited Wi-Fi with The Cloud and BT Openzone on all plans, and remember, O2 will not start capping 3G data until October - until then go nuts.