I had lot of enthu to upgrade iPhone 3 0s to Iphone 4 OS when it came out butI was not happy for long. Just to name few I could not surf net when playing songs. Both ipod and browser used to crash. After skimming through some third party support pages I hoped for re-start to help but no luck. This morning I went to apple support discussion and found almost 86 pages on Iphone 3g discussing on the same. The steps listed out there work out very well for me to re-store back it to 3 Os. Now I feel that my iphone works at blazing speed.
Before you start on the following steps download .net 4 framework and iphone 3 firmware.
Follow the steps below to re-store your iphone at your own risk..
1.Switch off your iphone using sleep button and sliding power off display
2.Hook u your iphone to your computer
3. Hold home and sleep button together at the same time for 10 seconds
4.After 15 seconds just take your hands off the sleep button and keeping the home button still down for another 15 seconds.
5. This would start your iphone in the recovery mode and you would see the prompt on the itunes for the same.
6. If you don't get this try step 3-5 again
7. After you get the recover option with the shift key down click on rest0re button and navigate to the folder where you downloaded iphone 3 firmware. It'd take 15 minutes to restore
8.If iTunes throw an error after re-storing you can exit the restore mode by pressing the home and sleep button for ten seconds.
8.After it's restored you can restore all your contacts from back up (back up you took before you upgraded to iphone 4.
I followed the above steps and it worked for me.