Hi Shelster - i went into store and just bought the iphone and took it home. I have found in the past unfortunately that most store staff are pretty useless (of course this is not true of all of them), but I tend to prefer calling.
If you registered with o2 before 19th september, then go for it. Buy the iphone, activation is done by yourself:
1. Update itunes to latest version
2. Plug iphone in - activation automatically starts
3. Select migration (it'll be obvious), basically moving your contract over. You'll need to put your mobby number in.
4. Select the tariff etc.
Now, mine activated in about 5 minutes, and my iphone was ready to use on my number
Edit: if you registered after 19th september you have to pay a 200 pound contract cancellation charge, BAH!
v.simple really.
Edit 2: Warning, the first o2 shop i tried was out of stock, fortunately Kingsotn has two
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