South Korea's LG Uplus to launch free SIM replacements with random IMSI

LG Uplus says it will start free SIM card replacements and resets for all subscribers on April 13 to implement a new random IMSI system. The plan covers users on LG Uplus’ network, including MVNO customers, smartwatches, and kids’ phones.

The change centers on IMSI, a 15-digit subscriber identifier used during network authentication. The last 10 digits have been linked to a subscriber’s phone number, raising concerns about targeted hacking. LG Uplus says it will randomize IMSI values, and notes that 5G networks use SUCI, a concealed IMSI, for added security.

Critics point out the company has not explained how it will assist digitally vulnerable groups—such as users in remote, mountainous areas or elderly customers who struggle with stores and service centers. No concrete plan has been announced for outreach or support to these customers.

LG Uplus has not disclosed how many SIM cards it holds for the replacement rollout, leaving questions about supply and logistics as the April deadline approaches.

Government data shows LG Uplus had about 10.47 million mobile and tablet subscribers at the end of last year. By contrast, rivals SK Telecom and KT have introduced certain measures for vulnerable customers—such as home visits or mail-based replacements—but neither achieved complete replacement across all customers.

LG Uplus emphasizes that IMSI alone is unlikely to trigger security breaches because authentication keys are encrypted and protected, and the 5G SA standard also encrypts IMSI transmission through SUCI. Nevertheless, the company has faced security scrutiny after a previous hacking episode, prompting ongoing concern among subscribers and regulators.

The government’s joint investigation with the industry confirmed some server-related data exposure at LG Uplus but said a full probe was hampered by ongoing OS upgrades and system changes, and it referred the matter to police. Consumer groups warn that the possibility of broader personal data leakage cannot be ruled out and called on LG Uplus to offer early-term contract waivers for customers wishing to cancel ahead of the SIM changes.

LG Uplus says it will publish a concrete plan for how the SIM replacement will be carried out in the coming days, ahead of the April 13 start date.