IMEI and ESN Basics Guide
What IMEI and ESN numbers represent, where to find them on any device, when to use each, and the common situations where dealers verify them.
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IMEI and ESN numbers run through nearly every wireless transaction — activations, unlocks, trade-ins, insurance claims, blacklist checks. This guide explains what each number actually represents, where to find them on different devices, when to use IMEI versus ESN, and the most common situations where dealers need to read or verify these numbers correctly. It's foundational reference for any wireless retail employee.
What These Numbers Are
Every phone carries a unique hardware ID. It's how carriers identify the physical device — separate from the SIM, the phone number, or the customer account.
There are two you'll encounter:
IMEI — International Mobile Equipment Identity. A 15-digit number. Used by GSM phones and essentially all modern devices.
ESN — Electronic Serial Number. An older 11-digit number. Used by older CDMA devices.
Key point: Almost every phone you handle today uses an IMEI. ESN only comes up with older CDMA hardware. When in doubt, it's an IMEI.
How to Find the Number
There are several ways to pull a device's IMEI or ESN. The fastest works on almost any phone.
The universal method
Open the phone dialer and enter:
*#06#
The IMEI (and ESN, if the device has one) appears on screen instantly. No menu digging, works on most phones regardless of brand or lock state.
Other places to find it
Phone settings — "About Phone" on Android, or General → About on iPhone
Original packaging — printed on the box barcode label
SIM tray — laser-etched on the tray itself on most iPhones
Behind the battery — on older devices with removable batteries
Back of the device — printed on the housing of many older phones
Dealer tip: When a phone is locked, damaged, or won't power on, the box barcode or the SIM tray etching saves you. Always check there before telling a customer the number can't be retrieved.
When to Use IMEI vs ESN
For nearly every modern transaction, you'll use the IMEI. The number comes into play across the whole range of wireless retail work:
Activations — the carrier ties service to the device's IMEI
Unlock requests — carriers process unlocks against the IMEI
Trade-ins — the IMEI identifies the exact device and its eligibility
Insurance claims — claims are filed against the insured device's IMEI
Blacklist and status checks — status is looked up by IMEI
ESN only matters when you're dealing with an older CDMA device that predates IMEI use. If a customer brings in a modern smartphone, you will use the IMEI.
Checking IMEI Status — and Why It Matters
Before you accept a trade-in or activate a used device, check the IMEI status. This is one of the most important habits in used-device handling.
An IMEI can come back blacklisted, which means the device was reported lost or stolen, or was left with an unpaid balance. Carriers refuse to activate blacklisted IMEIs.
Watch out: If you accept a blacklisted device as a trade-in, you've taken in hardware you can't resell or activate. If you try to activate one for a customer, the activation fails and you've wasted everyone's time. Check status first, every time, on any used device.
Duplicate IMEIs are a red flag
Every legitimate device has a unique IMEI. If you ever encounter two phones showing the same IMEI, that points to a counterfeit or tampered device.
Key point: Treat a duplicate IMEI as a major red flag. Counterfeit and tampered phones bring legal and activation problems — walk away from the transaction entirely.
Related WDG Resources
Pricing a buyback? Run the numbers with the Trade-In Value Calculator.
Need repair or unlocking vendors? Browse the WDG Vendor Directory.
Quick Reference
IMEI = 15-digit ID, used by modern and GSM devices
ESN = 11-digit ID, used by older CDMA devices
Dial *#06# to display the number on almost any phone
Also found in settings, on the box barcode, the SIM tray, or behind the battery
Modern transactions — activations, unlocks, trade-ins, claims — all use the IMEI
Always check IMEI status before accepting a trade-in or activating a used device
Blacklisted = reported lost/stolen or unpaid; carriers won't activate it
Duplicate IMEIs mean a counterfeit or tampered device — avoid the transaction
What this IMEI and ESN Basics Guide helps you do
IMEI and ESN numbers run through nearly every wireless transaction - activations, unlocks, trade-ins, insurance claims, and blacklist checks. This free guide explains what each number actually represents, where to find them on different devices, when to use IMEI versus ESN, and the most common situations where dealers need to read or verify these numbers correctly. Foundational reference for any wireless retail employee who touches activations, trade-ins, or device checks.
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IMEI and ESN Basics FAQ's
What is an IMEI number?
IMEI stands for International Mobile Equipment Identity - a unique number that identifies a specific cellular device. It is used in activations, unlocks, trade-ins, insurance claims, and blacklist or blocklist checks. You can usually find it by dialing star-pound-zero-six-pound, or in the phone's settings, on the SIM tray, or on the original box.
Both identify a device, but IMEI is used on GSM and modern networks, while ESN (Electronic Serial Number) and its successor MEID were used primarily on older CDMA devices. Today the IMEI is the number you will use in the vast majority of transactions, but you may still encounter ESN or MEID references on older equipment.
What is the difference between IMEI and ESN?
How do I check if a device is blacklisted?
A blacklist or blocklist check uses the device's IMEI to see whether it has been reported lost, stolen, or unpaid. A blacklisted device generally cannot be activated. Always verify the IMEI status on a used or trade-in device before accepting it, since a blacklisted phone has little resale value and cannot be put back into service.
Where do I find the IMEI on a phone?
The fastest way is to dial star-pound-zero-six-pound on the device, which displays the IMEI on screen. You can also find it in the phone's settings under About, on the physical SIM tray on many phones, or printed on the original packaging. For trade-ins, confirm the on-screen IMEI matches the box.