First time rooting

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http://androidforums.com – Hi, this will be my first attempt at rooting. The rooting side of things looks OK (ish) thanks to the sticky guide, what I'm concerned about is if I have to unroot for warranty purposes. I don't intend to use any custom roms or anything (I'm rooting purely to gain more memory on my phone). Because I'm not using any customs roms would unrooting be a simple process? I'm on o2UK if that makes a difference Laymans terms please, new to all this:). Thanks (General)