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Essential Knowledge Before SIM Replacement
Recently, SK Telecom has implemented a free SIM card replacement service in response to the SIM information hacking incident. As a result, many customers are changing to new SIM cards.
However, some users have complained that "the balance of the mobile transport card has disappeared," "contacts are missing," and "KakaoTalk chats are not restored." These issues are causing significant inconveniences for customers, which necessitates caution.
Replacing the SIM card is not just a change of chip. If done without preparation, it can lead to data loss or app errors. To prevent these inconveniences, we have prepared important checks and a checklist to verify before and after the SIM replacement.
Mandatory Checks Before SIM Replacement: Transport Card, Contacts, App Backup
1. Check and Refund Remaining Balance of Prepaid T-money Transport Card
For prepaid transport cards, the balance information is stored on the SIM card, and it is automatically reset to 0 upon replacement.
In such cases, it is advisable to request a refund to your account via the mobile T-money app by navigating to [More] → [Balance Refund], or to replace the card after exhausting the balance.
If a refund is not necessary, consider reducing the balance to a small amount.
2. For Postpaid Transport Card Users: Delete Card and Re-register
If you have registered a postpaid transport card with Samsung Pay or Wallet, you do not need a balance refund. However, if you change the device, you may encounter authentication errors.
To prevent these issues, it is important to delete the card from the app before changing the device and re-register it after inserting the new SIM card.
3. Contact Backup
Contacts are mainly stored on smartphones but can sometimes be stored on the SIM card.
If you are using an Android device, you can open the [Contacts] app, click [≡ Menu], go to [Contact Management], and select [Export] to save it as a .vcf file in the internal storage. Save it in this manner before replacing the SIM card.
iPhone users can check if they can back up by going to the [Settings] menu, selecting [Contacts], and then checking the [Import SIM Contacts] option.
4. KakaoTalk Chat Backup
Even if you replace the SIM card, the chat contents will not automatically be deleted. However, it is wise to prepare for unexpected situations.
Therefore, it is safe to backup your data in advance through [KakaoTalk Settings] → [Chat] → [Chat Backup].
Temporary backups can be restored within 14 days, and if you want backups that include photos and videos, you will need to subscribe to the paid service called ‘Talk Drawer Plus’.
SIM Replacement Checklist (Pre, During, and Post Steps)
By following the steps below, most inconveniences can be prevented during the SIM card replacement.
✔ Before Replacement (Prior to Power Off)
| Item | What to Do |
| Prepaid T-money | T-money app → [More] → [Balance Refund] or Exhaust Balance |
| Postpaid Transport Card | Delete from Samsung Wallet/App before replacement |
| Contacts | Android: Export as .vcf file / iPhone: Import SIM Contacts |
| KakaoTalk | Temporary Chat Backup in Settings (Restorable within 14 days) |
| SIM Protection Service | Check subscription status; shorten waiting time during online reservation |
✔ During Replacement
Turn off the smartphone, remove the existing SIM card, and insert the new SIM card. Then turn it on. If the data connection does not work, it is advisable to reboot after 1-2 minutes. Checking the PIN and PUK numbers provided in-store along with the replacement guide messages is also important.
✔ After Replacement
| Item | What to Do |
| T-money | Confirm recognition of new SIM after running the app → Register for charging/regular ticket |
| Contacts | Import contacts from internal storage (select .vcf) |
| KakaoTalk | Log in after running the app → Select backup file to restore |
| Financial/Certification Apps | Re-install joint/simple certificates, re-register card authentication, etc. |
| Confirm Completion of Replacement | Check completion in the T-world reservation confirmation page |
Key Summary for Safe SIM Replacement
The balance of transport cards will disappear with the SIM.
Contacts must be backed up as .vcf.
KakaoTalk can be backed up without worry.
Recently, due to the free SIM replacement service provided by SKT, many users are experiencing the hassle and complexity of SIM replacement.
However, by faithfully following the provided checklist, you can use the new SIM without data loss.
To avoid unnecessary confusion and inconvenience, it is advisable to check your smartphone now and prepare in advance.
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