I was planning to use my old iPhone 3GS for weekend project but I discovered that the screen was popped out and the back was bulging, I took it apart and this
Apple iPhone 3GS specs - PhoneArena
For Iphone 3gs Battery ,original Fast Shipping, Wholesale Or Retail - Mobile Phone Batteries - AliExpress
The Second Coming: Ars goes in-depth with the iPhone 3G | Ars Technica