I still have a 3G and upgraded to iOS4 – which slowed mine to a crawl. It turns out that the Spotlight search feature was the main culprit. If you turn that off (which most people don’t use anyway), your iPhone will speed up drastically. It won’t be the same as iOS3.x, but it will be much better.
Here are the instructions:
- Settings..Home Button…Spotlight Search
- Uncheck everything
- Hard reset the phone twice
To perform a Hard Reset, press and hold the Home and Sleep/Wake buttons on your iPhone at the same time for 10-20 seconds. After a few seconds the Slide to Power Off notice will appear, ignore this and keep holding down both buttons. In another few seconds the device should abruptly turn off, followed by the Apple logo and a reboot. Now release the buttons.
If your iPhone remains powered off, wait about 15 seconds then boot the phone by pressing the Sleep/Wake button.