ESN (Electronic Serial Number)

The Electronic Serial Number (ESN) is a unique device identifier used on CDMA mobile networks (historically Sprint and Verizon in the US) prior to the industry-wide adoption of the IMEI standard. For practical purposes in a modern buyback or resale operation, ESN and IMEI serve the same function: they uniquely identify a mobile device and can be checked against carrier blacklists to determine whether the device is eligible for activation and resale.

Most modern smartphones — including all devices released after approximately 2014 — use IMEI as their primary identifier. ESNs were used on legacy CDMA-only handsets, and while CDMA networks themselves have been largely decommissioned in the US (Sprint shut down its network in 2022; Verizon's CDMA network closed in 2022), legacy ESN references still appear in the vocabulary of US buyback and resale operations.

For buyback operators, the practical takeaway is that whether a device is identified by IMEI or ESN, the check process is the same: verify the identifier against applicable blacklist databases before purchasing the device. Tools such as the CTIA's Device Check, the carriers' own unlock/blacklist portals, and third-party IMEI/ESN checking services cover both identifier types for US networks.

When evaluating wholesale lots, manifests from US sellers may list both IMEI and ESN for legacy CDMA devices. A clean ESN (not blacklisted, not reported stolen, no outstanding balance) is the same commercial qualifier as a clean IMEI. A blocked ESN — even on a device with a clean IMEI — prevents the device from being activated on the relevant carrier network, which limits its resale value in the US market.