If you are uncertain what iPhone model or iPhone version you are using, you can find out with either a few clicks or by examining the exterior of your device. The iOS on your iPhone determines what software is compatible with your device. What iPhone model you are using determines what hardware is compatible with your device and what iOS version your device will support. You could use the SIM card tray to distinguish some iPhone models, but it doesn't work for all of them.
Tap the "Settings" app.
Tap "About." The iOS version installed on your iPhone is located to the right of Version.
Turn the iPhone over so you can see the back of the device. If there is a serial number etched into the lower half of the device, you are using an original iPhone.
Turn your iPhone over so you can see the back of the iPhone. If the Apple logo is silver and appears on the upper half of the iPhone, but the information on the lower half of the iPhone is faded and almost matches the black color of the rest of the back of the iPhone, you are using an iPhone 3G.
Turn your iPhone over so you can see the back of the iPhone. If the Apple logo and the information on the lower half of the device are silver but there is no serial number on the lower half of the device, you are using an iPhone 3Gs.
Look at your iPhone's edges. If the edge of the iPhone is flat, silver and wraps around the device, you are using an iPhone 4. Also, an iPhone 4 has two buttons on the upper-left edge, one with a "+" sign and one with a "-" sign, that let you control the volume. On other iPhones, the volume button is in the same location but it is just one button with two sides, like a rocker switch.