Iphone Serial Number Check
If you have an older iPhone, including the iPhone 3G, 3GS, 4GSM, or 4S, just pop open the SIM tray and you'll see your phone's serial number etched into the back of the tray. For Newer iPhones For iPhones after the 4S, the serial number is no longer etched separately on the SIM tray.
For the past two years, Apple's iPhone line has been sporting glass backs devoid of any of the old legal warnings or information — at least in the United States. But that can make it harder to find out things like your iPhone's model number. 
Iphone Serial Number Checker
Since different iPhone models support different carriers and bands around the world, if you're planning to use your iPhone in other countries, if you're interested in CDMA (Verizon/Sprint) compatibility, or you just prefer Qualcomm or Intel modems, it's important information to know. Here's how to find it.