Dual SIM functionality allows you to insert two SIM cards into a single smartphone, offering a variety of uses. Here, we’ll introduce recommended uses and examples of what to avoid.
Good ways to use dual SIMs and examples
1. Separate phone numbers for work and personal use.
- Advantages：
- One smartphone can handle both work and personal use.
- You can use calls and SMS separately.
- It’s easy to manage phone books and apps separately (some apps allow profile switching).
- Example of use：
- A salesperson uses both a company-issued SIM (for work) and a personal SIM simultaneously.
2. Using both domestic and international SIM cards
- Advantages
- When traveling or on business trips abroad, insert a local SIM card to enjoy affordable communication.
- You can also keep your Japanese SIM card and use it for receiving SMS messages and two-factor authentication for banking.
- Example of use
- Use a Japanese SIM card plus a local prepaid SIM card (such as AIS in Thailand) to use local data communication.
3. Using separate lines for data communication and voice calls.
- Advantages
- Save money on voice calls with a budget-friendly calling plan and on data communication with a high-capacity SIM card.
- Example of use
- A combination of Rakuten Mobile (unlimited voice calls) and IIJmio (20GB data only).
4. Use different carriers depending on whether you’re in an urban or mountainous area.
- Advantages
- It can compensate for weaknesses in the communication area.
- Example of use
- With two SIM cards, one from SoftBank and one from Docomo, you can maintain a connection with the other even if one is out of range.
5. eSIM for calls, physical SIM for data communication.
- Advantages
- eSIMs can be switched using profiles, making them ideal for users who frequently switch between SIMs.
- Example of use
- eSIM with LINEMO (calls/SMS) + physical SIM with IIJmio (data communication).
Examples of things you should not do and points to be aware of.
1. Dual SIM usage with the same phone number (duplicate contract)
- Normally, it’s not possible to use one phone number on two SIM cards simultaneously.
–Even when using both a physical SIM and an eSIM simultaneously, the phone numbers must be different.
2. Without clearly defining the purpose, it can lead to confusion.
- It becomes difficult to track which SIM card is being used for communication and calls, making billing and communication management complicated.
–Solution: Assign a clear role to each SIM and specify the preferred SIM in the settings.
3. Be aware of potential communication interruptions and roaming issues when switching SIM cards.
- There is a possibility of temporary communication interruptions, especially when switching data SIMs.
- Choosing the wrong SIM card overseas could result in high roaming charges.
4. Frequent reissuance of eSIMs may result in restrictions.
- Depending on the carrier, reissuing an eSIM profile may incur a fee or have a limit on the number of times it can be done.
5. Some models have unstable communication.
- In particular, with models that do not support DSDS (Dual SIM Dual Standby) or DSDA (Dual SIM Dual Active) specifications, one SIM may lose connection while the other is working.
–It is best to choose a newer model.
