LG Uplus to replace IMSIs tied to phone numbers in security upgrade

At the Mobile World Congress in Barcelona, LG Uplus disclosed that its SIM identity numbers (IMSI) are issued based on customers’ phone numbers, a practice that makes the IMSI easier to link to a specific user than the randomized approach used by SK Telecom and KT. The company also announced a broad security upgrade, including free SIM replacements for all customers.

IMSI stands for International Mobile Subscriber Identity, a 15-digit number used to identify users in mobile networks. When linked with other data, it can enable security threats such as counterfeit handsets or SIM-based fraud.

LG Uplus said its current IMSI method complies with international standards and is safe, but given the rising frequency of major security incidents, the company decided to act.

Starting April 13, LG Uplus will deploy a strengthened security system and proceed with free SIM exchanges and reconfigurations for all customers, in a staged rollout. The company says the process will aim to minimize customer disruption.

The company described its IMSI as formed from a 15-digit code consisting of country code, operator ID, and subscriber identifier.

LG Uplus noted that since 2011, when Korea launched 4G, its IMSI issuance has been tied to subscribers’ actual phone numbers, whereas SKT and KT used a randomized approach. It attributed the difference to older radio-frequency technologies used during the 2G/4G transition when international standards were still evolving.

LG Uplus began security reviews in June last year and updated its systems in November to allow IMSI to be reset without physical SIM replacement; this year they plan to encrypt IMSI in 5G standalone (SA) operation to bolster security.

Lee Jae-won, vice president and head of LG Uplus’s consumer division, said the company would prepare to minimize any inconvenience to customers during the update.

For U.S. readers, the move highlights ongoing global efforts to harden mobile identities as 5G networks expand and cross-border roaming grows. IMSI security matters for the risk of SIM-based fraud and device cloning, with potential implications for U.S. telecoms, multinational carriers, and the broader security of mobile networks and related supply chains.