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From keeping transit card balances to saving contacts, here's some tips before swapping your SIM card for SK Telecom users

Published: 29 Apr. 2025, 17:29

A SK Telecom retail store employee changes the SIM card for a phone at a branch in Seoul on April 28. [YONHAP]

SK Telecom is offering a free subscriber identity module (SIM) card replacement service to protect its subscribers from recent hacking attempts. However, some users who have swapped their SIMs have reported issues such as their “transit card balance showing as zero” or that their “contacts disappeared.”

To help prevent these problems, here’s what you need to know before and after changing your SIM.

Transit card balance: Refund required through app

If your transit card balance appears as zero after changing your SIM, it’s not an error. It’s an expected result of how SIM cards work. Prepaid transit cards like Tmoney store balance information directly on the SIM through near-field communication technology. When you replace the SIM, that stored information disappears, resetting the displayed balance to zero.

To avoid losing your balance, you should request a refund through your transit card app before replacing your SIM. In the Tmoney app, you can tap the “More” button indicated by three dots on the home screen, select “Refund,” and enter your bank account details to receive the balance.

If you have only a small amount remaining, it might be easier to use up the balance before switching your SIM. Refunds are also available at some convenience stores and Tmoney customer centers. For postpaid transit cards, users should delete the card information before replacing the SIM and then reissue the card after installation, as there is no stored balance.

Saving contacts: Export first, then import

Most contacts are saved on the phone itself, but some devices also store contacts on the SIM. To be safe, you should back up your contacts to your device before swapping the SIM.

For Samsung users, go to the “Contacts” app, tap the three-line menu button, select “Manage contacts,” and then tap “Export” to save them to the device's internal storage. After replacing the SIM, use the “Import” option to retrieve them.

iPhone users can navigate in this order: "Settings," "Apps," "Contacts" and "Import SIM Contacts" — and then select where to import the contacts when prompted. If these options don’t appear, Apple advises contacting your device’s manufacturer for further assistance.

How to back up KakaoTalk chats

Replacing your SIM won’t delete your KakaoTalk chat history. Still, if you're concerned, you can use KakaoTalk’s backup features.

Open the KakaoTalk app, tap the gear icon to enter “Settings,” then select “Chats.” You can choose either the paid “Auto Backup” for chats and media or “Temporary Backup” for chat-only data. Temporary Backup saves text chats, allowing you to restore them within 14 days of reinstalling the app, and it’s free.

If you also want to back up photos, videos, and other media, you’ll need a subscription to the paid service, “KakaoTalk Locker Plus.”

Translated from the JoongAng Ilbo using generative AI and edited by Korea JoongAng Daily staff.
BY KIM JI-HYE [[email protected]]