How can I fix slow iOS 4 on my iPhone 3G?
Many iPhone 3G users who updated their firmware to iOS 4 have reported problems including sluggish performance, decreased battery life, and excessive heat coming off their device.
One temporary fix has been discovered and my help in some cases. The change is fully reversible and can be initiated with the following steps:
1. Navigate to Settings -> General -> Home Button -> Spotlight Search
2. Deselect every option in the list.
Many iPhone 3G users have reported improvements in speed after making this change. Apple is working on an iOS 4.1 update that is said to correct performance and battery issues on the iPhone 3G.