Tried this IOS a few months ago and it didnt offer me anything over my jailbreak. Once its jailbreakable though i will update as the folders was nice.
Have you tried 4.1 with the jailbreak yet, or are you still on 3.2.2 If you haven't - give it a go, it's well worth it. I'm waiting for a jailbreak on 4.2 before I put that on my iPhone4 as I like the things the jailbreak can do. I would miss the ability to switch on/off bluetooth and wi-fi quickly and the one tap turn-off of all open apps. There's loads more, but they are the main ones I use.
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There are only two things I can think of (that I will use) on the phone that 4.2 gives, where's my iphone and the printing. I've done the iPad update, phone will wait!
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TonyZ