You can the serial number on an iPhone in a few different ways. For most models of iPhone, figuring out how to find the serial number is as simple as opening the Settings app. For older models, it's on the SIM tray or the back of the phone. If you can't turn on your iPhone, you can also get the serial number from the Apple ID web page, or another iOS device using the same Apple ID. If you saved the original packaging, you can also find the iPhone's serial number on the barcode sticker on the box