To remedy the sluggish performance (or at least one cause of it) go to “Settings - General - Home Button - Spotlight Search - deselect every option” and this will stop background indexing on the phone. Several users reported that the fix showed immediate results on the iPhone 3G. its worth a try!
[Via]
<a href="http://dailyiphoneblog.com/2010/07/31/guide-how-to-fix-sluggish-ios-4-performance-on-the-iphone-3g/">

[Read the original blog post]
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