How to identify Iphone models?

There's some characteristic and specification either physical or operational specification we can list, check that out:
  Identifying features


iPhone 4S
The model number on the back cover is: A1431 on the iPhone 4S (GSM China) A1387 on the iPhone 4S The front and back surfaces are flat and made of glass. There is a stainless steel band around the edges. The volume up and down buttons are marked with a "+" and "-" sign. There is micro-SIM tray on the right side that holds a micro-SIM card.

  iPhone 4
The model number on the back cover is: A1349 on the iPhone 4 (CDMA model) A1332 on the iPhone 4 (GSM model) The front and back surfaces are flat and made of glass. There is a stainless steel band around the edges. The volume up and down buttons are marked with a "+" and "-" sign. The GSM model has a micro-SIM tray on the right side that holds a micro-SIM card. The CDMA model does not have a SIM tray.

iPhone 3GS

The model number on the back case is: A1325 on the iPhone 3GS (China) A1303 on the iPhone 3GS The back case is made of plastic. The imprint on the back case is the same bright and shiny silver as the Apple logo. The serial number is printed on the SIM tray.

iPhone 3G

The model number on the back case is: A1324 on the iPhone 3G (China) A1241 on the iPhone 3G The back case is made of plastic. The imprint on the back of the phone is less shiny than the Apple logo above it. The serial number is printed on the SIM tray.

iPhone

The model number on the back case is A1203. The back case is made of metal. The serial number is etched in the back case.

Important: Information about products not manufactured by Apple is provided for information purposes only and does not constitute Apple’s recommendation or endorsement. Please contact the vendor for additional information.