Instructables
Picture of Fixing cracked glass on iPhone 3g/s
If you have ever experienced the pain and despair of picking your once shiny iPhone off the ground to find a disgusting fissure across the screen? Don't panic, if you are reading this, you have probably already been turned away by your local Apple store. With the replacement part, a steady hand, and little bit of luck, your phone can be as good as new! I would rate this process as moderately easy, assuming you have some basic tinkering experience or technical knowledge. I accept no responsibility for the damage you may or may not inflict on your iPhone while performing this tutorial. I highly recommend that anyone attempting this process, carefully read through my entire tutorial before proceeding at their own risk. 

NOTE: This tutorial is done with an iPhone 3gs but the process is EXACTLY the same for the 3g, a specific replacement digitizer is required for the 3g however. 
 
Remove these adsRemove these ads by Signing Up

Step 1: Materials and Tools needed

Materials

1. Replacement Digitizer for Iphone 3g(s)
2. Iphone with damaged digitizer(glass)
3. Phillips Head screwdriver size #00
4. Jeweler size flathead screwdriver
5. Suction Cup
6. Hairdryer (not pictured) 
7. 3m double sided sticky tape  

Step 3: Separating Screen from Bottom Case

Picture of Separating Screen from Bottom Case
Secure the suction cup to the bottom half of the screen and gently pull up to separate the touch screen assembly from the body of the phone. Be careful not pull on the ribbon cables that connect the two pieces of the phone under the the ear piece.

Step 5: Removing LCD

Remove the 6 screws that hold the LCD to the digitizer. There are 3 on the left, 2 on the right and 1 on the back near the top.
I was doing this and I pulled too hard on the suction cup. The ribbon thing ripped. I'm guessing I should say goodbye to that phone. :( HELLLP
You can just buy a new screen and digitizer assembly. it shouldn't be much more than 20 bucks.