ESN vs IMEI: What Is the Difference and How to Check Both
When buying or selling a used phone, you'll encounter two important device identifiers: ESN and IMEI. While both serve as unique identifiers for mobile devices, they're used by different network technologies and have different implications for buyers.
What Is an IMEI Number?
The IMEI (International Mobile Equipment Identity) is a 15-digit number assigned to every device that uses GSM, UMTS, or LTE networks. It's the global standard used by most carriers worldwide.
- Length: 15 digits (sometimes 17 with software version)
- Format: TAC (8 digits) + Serial (6 digits) + Check digit (1 digit)
- Used by: AT&T, T-Mobile, international carriers, all modern 4G/5G devices
- Dual SIM phones: Have two IMEI numbers — one per SIM slot
How to Find Your IMEI
- Dial
*#06#from the phone dialer - Check Settings → About Phone → IMEI
- Look on the SIM card tray
- Check the original box sticker
What Is an ESN?
The ESN (Electronic Serial Number) is a 32-bit identifier (shown as 8 hex digits or 11 decimal digits) originally used by CDMA network devices. It was the standard for carriers like Verizon and Sprint before the industry transitioned to LTE.
- Length: 8 hexadecimal digits or 11 decimal digits
- Used by: Legacy CDMA devices on Verizon, Sprint (now T-Mobile), US Cellular
- Status: Largely deprecated — replaced by MEID and IMEI on modern devices
MEID: The Bridge Between ESN and IMEI
The MEID (Mobile Equipment Identifier) is the 56-bit successor to ESN. It's essentially the CDMA equivalent of IMEI:
- Length: 14 hexadecimal digits
- Relationship to IMEI: On modern phones, MEID is the first 14 digits of the IMEI
- Modern devices: Nearly all phones manufactured after 2015 use IMEI exclusively, even on former CDMA carriers
ESN vs IMEI: Key Differences
| Feature | ESN | IMEI |
|---|---|---|
| Network type | CDMA only | GSM / LTE / 5G (universal) |
| Length | 8 hex / 11 decimal digits | 15 digits |
| Global standard | No (US-centric) | Yes (worldwide) |
| Still in use | Mostly deprecated | Yes — universal standard |
| Blacklist checking | Carrier-specific only | Global GSMA blacklist |
| SIM card required | No (CDMA is SIM-less) | Yes (GSM uses SIM) |
| Carrier flexibility | Locked to one CDMA carrier | Can be unlocked for any carrier |
What Does "Bad ESN" or "Bad IMEI" Mean?
When someone says a phone has a "bad ESN" or "bad IMEI", it means the device identifier has been flagged by the carrier. Common reasons include:
- Unpaid balance: The original owner stopped paying their installment plan
- Reported stolen: The device was reported lost or stolen
- Insurance claim: An insurance replacement was issued and the old device was blacklisted
- Fraud: The device was obtained fraudulently
A phone with a bad ESN/IMEI cannot be activated on the reporting carrier's network, and may be blocked internationally through the GSMA global blacklist.
How to Check ESN and IMEI Status
Free Methods
- Verimei Free IMEI Check: Instant IMEI verification including blacklist status, carrier info, and SIM lock status
- Blacklist Check: Specifically checks if the IMEI is on the global stolen/lost database
- Carrier tools: Verizon, T-Mobile, and AT&T have online IMEI check pages (limited info)
What to Check Before Buying
- Blacklist status: Is the phone reported stolen or lost?
- Carrier lock: Is it locked to a specific carrier?
- Finance status: Does it have outstanding payments?
- Activation status: Can it be activated on your preferred network?
Do Modern Phones Have ESN?
Short answer: No. Since the US industry completed its transition from CDMA to LTE/5G, all modern smartphones use IMEI exclusively. Even Verizon — historically the largest CDMA carrier — shut down its CDMA network in 2022 and now requires all devices to have IMEI.
If you encounter a phone that only has an ESN and no IMEI, it's a very old device (pre-2015) that will not work on any current US network.
Bottom Line
For any phone purchase in 2026, IMEI is the only number you need to worry about. Run a free IMEI check on Verimei before buying to verify the phone isn't blacklisted, stolen, or carrier-locked. It takes 30 seconds and could save you from a costly mistake.
