You don't need to get a contract with AT&T or o2. You just need the phone.
I purchased quite a few with v1.1.1 software and all I needed was
iNdependence and
anySim.
Just google for them. The iNdependence software has all the instructions. You have to download the 1.0.4 software from the Apple website and rename the file. After that, iNdependence downgrades the phone to 1.0.4 and then you can jailbreak it. You then upgrade to 1.1.1 with iNdependence and finally you upload anySim to the phone and run it and then you have an activated iPhone that works with any sim from any network.
Takes about 30 minutes and involves restarting the iPhone several times.
v1.1.2 isn't that crackable just yet but it is not necessary as the only differences are some international keyboard layouts.
Once unlocked with iNdeoendence you can add many different apps and can customise the phone to your hearts content. Just use google and a bit of common sense.