Whilst the Orange & O2 deals DO look very similar.. Orange has a very low (but allegedly rarely enforced) data cap.
The below is from Oranges iPhone site
Separate Fair Usage policies of 750MB / Month apply to both
BT Openzone Wi-Fi and Mobile Internet Browsing. See terms for full details.
Tesco Mobile is getting the iPhone & apparently by Christmas. It's mobile network uses O2 & they promise "]ompetitive" tariffs.
Vodafone will be offering the iPhone in the early part of new year.
And, if you already have an iphone but didn't know. O2 are now offering an Official Unlock