You'll have to pay money up front. You won't get an iPhone as a "free" upgrade unless you have a very high monthly tariff.
---------- Post added at 23:09 ---------- Previous post was at 23:09 ----------
O2 has finally put some information up!
http://www.o2.co.uk/iphone/iphonetariffs/
Prices are similar to the rest, e.g.
- 24 month contract at £31 per month for 600 mins plus "unlimited" SMS, with a £6 per month 500MB Data Bolt On (O2 split the data off a while back) [£37 per month total]: 16GB 4S costs £99 up front.
- 18 month contract at £31 per month for 600 mins plus "unlimited" SMS, with a £6 per month 500MB Data Bolt On [£37 per month total]: 16GB 4S costs £169.99 up front.
Data Bolt Ons include the "Visual Voicemail" and also tethering (tethering used to be a separate thing).
Existing customers can also choose from a range of 12 month contracts.
So, if you compare:
e.g. a 24 month "~£35ish" contract, you get 600 minutes, "unlimited" SMS, and 500MB data from O2 for £37, Orange for £36, T-Mobile for £35.75, and Vodafone for £36. Upfront cost of a 16GB 4S with each is £99 for O2, £99.99 for Orange and T-Mobile, and £159 for Vodafone (who will give £59 back, but only if pre-ordered today, according to the site). With Three, it's £35 per month for 2000 minutes, 5000 SMS, and truly unlimited data, with an upfront cost of £99.
http://www.o2.co.uk/iphone/iphonetariffs/
http://shop.orange.co.uk/newiphone
https://www.t-mobile.co.uk/shop/pay-...mobile-phones/
https://www.vodafone.co.uk/brands/ip...hone/index.htm
http://www.three.co.uk/Phones/Preorder