Android phone users can locate the IMEI by selecting settings from the menu, then selecting About Phone, then Status. IPhone users can find the IMEI by going to the Settings menu, then selecting General, then selecting About.
IMEI stands for International Mobile Equipment Identity. IMEI numbers help service providers track stolen phones and deter mobile device theft internationally. An IMEI number is a device's unique 15-digit identification number. This number has no connection to the owner of the mobile device. The service provider uses the IMEI to identify the device for network purposes.
Websites such as IMEI.info can provide information about a device when the user provides the IMEI, including whether a device is locked to a carrier.