When your iPhone is working very slow and you're not beatific with your one’s. If you've download iOS 4 on your iPhone then ascertain that you do not edit your iPhone to iOS! If you need to speed up iPhone 3G then chase the following ways.

Difficult Reset your iPhone 3G:
Very hard reset will clear all caches, RAM buffers etc. from your iPhone 3G memory. Act the Hard Reset two times to get the required impact. In term to Hard Reset your iPhone 3G follows easy steps shown below:

a) Press-hold the button of Home and the Wake/Sleep button (on top of the iPhone) concurrently for 5 to 10 seconds.
a) Continue holds both buttons until the iPhone close and come to restart.
b) You may let go if you see the silver Apple logo.You've finished a hard reset victoriously.

Disable the backgrounds:
It might assure that while unlocking iPhone 3G on iOS 4 accessing software you've enabled backgrounds to provide the icons a good shadow effect. But the shadow processing gets a big amount of memory on your iPhone 3G creating it slack in performance. You can disable the backgrounds by updating a file to speed up iphone.
For mre information visit: http://www.fireebok.com/resource/how-to-speed-up-and-revive-your-iphone.html