To use a prepaid SIM, you check your device’s SIM lock status, insert the SIM card, and, depending on the product, complete activation and configure the APN (Access Point Name). The process is not difficult if you follow the steps in order, but if you do not check your device’s compatibility and the card’s specifications beforehand, you may be unable to connect even after inserting the card. This article covers preparation before you buy, the setup flow, and what to do when you cannot connect.
- Before using a prepaid SIM, check whether your device is SIM-locked and whether it is compatible
- You can buy at physical stores and airports, and you can also choose ahead of time from online shops
- After inserting the card, complete activation and APN setup by following the product’s instructions
- If you cannot connect, restarting your device or deleting existing profiles may help
- When buying, check the data allowance and expiry, as well as whether voice calls and top-ups are supported
Preparation Before Using a Prepaid SIM
To use a prepaid SIM you have bought, you need to check in advance that your smartphone can use another carrier’s network.
| Item | Key Point |
|---|---|
| SIM lock | Check that you can use another carrier’s network |
| SIM size | Choose the size that fits your device |
| Verified devices | Check supported bands and target models |
Check That Your Device Is SIM-Unlocked
Devices bought from a carrier may have a “SIM lock” that prevents you from using another carrier’s network. If the lock remains, you may see a message such as “Invalid SIM” and be unable to connect even after inserting a prepaid SIM. In that case, complete the unlock procedure in advance by following the guidance from the carrier you bought the device from. Note that, as a general rule, devices released in Japan from October 2021 onward are no longer SIM-locked from the start.
Choose the SIM Size That Fits Your Smartphone
SIM cards come in three sizes, standard SIM, microSIM, and nanoSIM, and the size that fits differs by device. Current smartphones mostly use the smallest, nanoSIM. With a “multi-cut SIM,” where you punch out the size you need from the card, you do not have to worry about choosing the wrong size.
Check That Your Device Is on the Verified Devices List
Even if your device is SIM-unlocked, you may be unable to connect, or the connection may be unstable, if the frequency bands your device supports do not match the network the SIM uses. On the official website of the prepaid SIM you plan to buy, check that your model is listed under “verified devices.”
Where to Buy a Prepaid SIM
Choose where to buy based on when you need to get online and how much time you have to prepare.
| Where to Buy | Key Point |
|---|---|
| Convenience stores and electronics retailers | You can see the product in person before buying |
| Online shops | Order ahead from a wide range of plans |
| Major airports | You can buy right after you arrive |
Buy at a Convenience Store or Electronics Retailer
At electronics retailers and some convenience stores, you can buy packages displayed in the store. This suits you if you suddenly need a connection or want to see the product before choosing. Products and stock differ by store, so it is reassuring to check in advance.
Order in Advance from an Online Shop
On Amazon or a provider’s official website, you can choose from plans with various data allowances and periods of use. Since the SIM is delivered to your home or a specified address, this is convenient if you want to arrange it several days before your trip or start date.
Buy from a Vending Machine or Shop at a Major Airport
At some international airports, vending machines and counters that sell prepaid SIMs to foreign tourists and people returning temporarily are set up in places such as the arrivals lobby. You can buy right after you arrive and get online, but the products and business hours differ by airport.
Steps to Use a Prepaid SIM
It is not just a matter of inserting the card, because depending on the product, you may need to complete activation and APN setup. Let us go through the steps in order.
| Step | Key Point |
|---|---|
| Step 1 | Turn off your device and insert the SIM card |
| Step 2 | Complete activation if required |
| Step 3 | Set the APN details as needed |
Step 1: Turn Off Your Device and Insert the Card
For safety, turn off your smartphone before you start. Use the included pin to pull out the SIM tray, line up the notch and set the prepaid SIM on the tray, then put it back into the device.
Step 2: Complete Activation If Required
Follow the steps on the package, such as calling a specified number or registering (activating) on a dedicated website. For products that require activation, you cannot connect to the internet until you complete it, even if your device is receiving a signal.
Step 3: Set the APN as Needed
To connect to the internet, you set the Access Point Name (APN) on your device. How to set it differs by device and by prepaid SIM product. On an iPhone you may use a configuration profile, and on an Android device you may enter the APN details manually. Follow the product’s instructions or the provider’s guidance when you set it up.
What to Do When You Cannot Connect to the Internet
If you still cannot connect after finishing the setup, or an error appears, check the following items in order.
| Item | Key Point |
|---|---|
| Re-acquiring the signal | Restart or toggle Airplane Mode |
| Mobile data | Check that the setting is on |
| Configuration profiles | Delete old settings and set up again |
Restart Your Device to Re-acquire the Signal
Right after you insert a SIM card, it may take a while for your device to recognize the new line. Restarting your smartphone or toggling Airplane Mode on and off makes it search for a signal again, and you may be able to connect.
Check That Mobile Data Is On
In your device settings, check that “Mobile Data” is not turned off. If you were working over Wi-Fi and went out with mobile data still off, you cannot connect to the internet.
Delete Existing Profiles and Set Up Again
If you have used another budget SIM (MVNO) on your iPhone in the past, an old APN configuration profile may prevent the new SIM from connecting. Open “VPN & Device Management” under “General” in the Settings app, delete the old profile, and then apply the new settings.
Points to Note When Choosing a Prepaid SIM
Choosing a product that fits how you will use it helps you avoid losing your connection during your stay or paying for things you do not need.
| Item | Key Point |
|---|---|
| Period of use and data allowance | Choose a plan that fits your stay and usage |
| Voice calls | Choose based on whether you need to make calls |
| Top-up availability | Check whether you can add data and the terms of use |
Check the Period of Use and Data Allowance Limit
A prepaid SIM has a fixed number of days and a data allowance limit, such as “5 GB for 15 days.” Before you buy, estimate whether the number of days covers your stay and whether the data allowance is enough for how you will use it, such as watching videos.
Check Whether It Is Data Only or Includes Voice Calls
Some prepaid SIMs for travelers are “data only” and can be used just for the internet. If you plan to make calls, for example to book a restaurant, it is safer to choose a product that supports voice calls.
Check Whether You Can Top Up (Add Data)
Prepaid SIMs include types that let you add data within the period of use, and types that simply end when the period expires. If your stay may be extended, choosing a product that supports top-ups can save you the trouble of buying a new SIM.
