Speeding up an iPhone 3G after upgrading to iOS4

If you find your iPhone 3G extremely slow after upgrading to iOS 4, a hard reboot - and turning off Spotlight search may help.

Doing a normal restart of the iPhone doesn’t seem to have any real effect. To force the iOS to rebuild properly, you have to press and HOLD the Sleep / Wake button together with the Home button for about ten seconds, which will initiate a proper reboot.

When it turns back on, it will take a while to boot. On iPhone 4, it boots from a cold restart in about 30 seconds, but on an older iPhone 3G, it might take more than four minutes starting up!

To turn off Spotlight indexing. Go to Settings > General > Home Button > Spotlight search and turn search indexing off for as many items as possible.

Hope this tip is helpful for some of you.