The International Mobile Equipment Identity (IMEI) is a unique 15-digit serial number assigned to every GSM, UMTS, and LTE mobile phone. It serves as a digital fingerprint for your specific device.
*#06#
Classic phones: To find the IMEI code on your phone, enter *#06# on your keypad when on the main screen. Nokia 1600 User Guide | Specialty Answering Service Nokia 1616-2 Imei Change Code