You can tell which iPhone model you have by navigating to Settings > General > About > Model.
Icon Model Year Introduced Model Number Capacity
iPhone 2007 A1203 4, 8, and 16 GB
iPhone 3G 2008 A1241 8 and 16 GB iPhone 3G (China) 2009 A1324 8 and 16 GB
iPhone 3GS 2009 A1303 16 and 32 GBiPhone 3GS (China) 2009 A1325 16 and 32 GB
iPhone
You can easily identify iPhone by the metal case and the serial number etched on the back.
iPhone 3G
You can distinguish iPhone 3G from iPhone by its plastic case. Additionally, the serial number is no longer on the back case imprint. You'll find the serial number for the iPhone 3G on the SIM tray. The imprint on the back of the phone has a faded look. Only the Apple logo is bright silver.
iPhone 3GS
You can distinguish iPhone 3GS from iPhone by its plastic case. Additionally, the serial number is no longer on the back case imprint. You'll find the serial number for the iPhone 3GS on the SIM tray. You can distinguish iPhone 3GS from iPhone 3G by the imprint on the back of the phone. The entire imprint on the back of iPhone 3GS is bright silver (not just the Apple logo).
