Cheap SIMs and Phone Plans in Japan 2026: How Much Data You Need and How to Switch (MNP)

Why cutting your phone bill isn't a one-time saving

Some ways to save money only work if you make an effort every time you shop. Others take one bit of work and keep paying off month after month. Reviewing your phone plan is a classic example of the second kind. If you're still on a big-data plan from a major carrier and move to a sub-brand or a cheap SIM, it's not unusual to save several thousand yen a month, or tens of thousands of yen a year. Switching is basically a one-off task, and the savings keep adding up every month you stay on the new plan.

But if you rush into the cheapest plan thinking "cheaper is always better," you may regret it. Your connection might crawl at lunchtime, the call package you needed might be missing, or you might lose your carrier email address. This guide covers the points where people most often trip up, in order. It starts with how Japan's mobile networks work, which is worth knowing before you compare price lists. It then covers estimating your data needs, choosing between brands, the practical steps of MNP (switching while keeping your number), and the pitfalls that have nothing to do with price. Terms for each service change often, so always confirm final prices and rewards on each company's official site.

Stop worrying every month and set a check-up day instead

At the end of this article we recommend a "yearly check-up, so switching isn't a one-and-done." Fixed costs won't go down on their own if you ignore them. But staring at them every month won't reveal anything new either. The fix is to decide how often you'll check first.

Some shopping works the same way. You don't need to think about it every time, but you won't notice problems unless you look now and then. Leave it alone, and the buying habits you set last year quietly carry on this year too.

1. Pick your check-up dayChoose a month that's easy to remember, such as your birthday month, your contract renewal month, or the start of the fiscal year.
2. Write down just three things to checkFor example: what's in your subscriptions and how often they arrive, what you pay for monthly, and the consumables you always buy at the same store. Add too many and you won't keep it up.
3. Act only on what you find that dayNarrow it down to one thing to fix on the spot. If you try to review everything, nothing ends up changing.
4. Don't think about it until the next check-up dayThis is the real point. Setting a day isn't so much about looking as it is about creating a stretch of time when you don't have to.

Set it up this way, and when you hear that prices have changed, you won't need to panic. Treat anything genuinely urgent, like expiring balances or cancellation deadlines, separately, and put those exact dates in your calendar. Regular deliveries are where check-ups pay off most, especially things where you can adjust the frequency and amount later (see choosing water and drink delivery or a water filter).

The basics: everything runs on four networks — docomo, au, SoftBank and Rakuten

Why are cheap SIMs cheap? Because they don't build their own cell towers. They rent capacity on the major carriers' networks. In the end, all mobile service in Japan runs on one of four networks: docomo, au, SoftBank and Rakuten Mobile. There may be dozens of brand names, but the actual signal comes from these four. Keep that map in mind and choosing gets much easier.

Here's one practical tip: pick the network that already works well for you, and you'll almost certainly be fine after switching. For example, if docomo works well at home and at work, choosing ahamo or a cheap SIM on the docomo network means you'll hardly need to worry about signal. On the other hand, if you're moving to a different network such as Rakuten Mobile, check the official coverage map to make sure the places you go are covered. That way you avoid the disappointment of having no signal once your line is active. See also our tips on checking coverage and signal.

The real difference between sub-brands and cheap SIMs shows up at lunchtime

Looking only at price lists, cheap SIMs (MVNOs) like IIJmio and mineo seem cheaper than sub-brands like Y!mobile and UQ mobile. So what causes that gap? The difference you'll feel most is speed at peak times.

Sub-brands are run by the major carriers themselves on their own networks, so speeds don't drop much even at weekday lunchtime (12:00–13:00) or during the evening commute. MVNOs, on the other hand, have a cap on the "width" (bandwidth) of the capacity they rent from the carriers. That's a built-in weakness: speeds can drop sharply on weekdays from 12:00 to 13:00, when everyone is online at once. You'll notice it as videos taking a while to start or maps loading slowly.

Your daily routine is the best guide. If you watch videos or do heavy tasks on your phone at lunch, or you're out and about relying on mobile data all day, a sub-brand or online-only brand is the safer choice. But if you're on office or home Wi-Fi during the day, you'll barely notice the MVNO weakness and get the full price benefit. For details on how they work, see how cheap SIMs (MVNOs) work and what to watch out for. For choosing between brands, see choosing between major carriers, sub-brands and cheap SIMs.

Don't guess how many gigs you need

The biggest waste in choosing a plan is overestimating how much data you need. Paying for gigs you never use is like chartering a bus that runs mostly empty. Start by checking your actual data usage over the past few months in your phone's settings (on iPhone: Settings → Cellular/Mobile Data; on Android: somewhere under Settings → Network). If you have Wi-Fi at home and work, that figure is exactly what you really need when you're out.

If you're unsure, starting one tier lower is the right move. If it's not enough, most companies let you add data 1GB at a time, and upgrading your plan is easy. Start with a big plan, though, and you may keep paying for leftovers without noticing. That said, if you find yourself buying extra data almost every month, the next plan up is almost always cheaper. We go into more detail in how much data (gigs) you need and how to choose.

One more thing people often miss: discounts for bundling with home fiber internet. Many sub-brands lower your monthly bill if you also use their group's home internet. Look at the total cost including home internet, not just the phone, and the best option may change. Consider it together with choosing home fiber internet.

Calls and point ecosystems: where your monthly bill goes up or down

Just as important as data are how you make calls and which points ecosystem you lean toward. Leave these until later, and the savings on your base plan can be wiped out by call charges.

Three call options, depending on how much you phone

• You mostly use LINE calls or other data-based calling apps: You don't need a call option. The base plan alone is cheapest.
• You sometimes make calls of a few minutes each: A "5-minute / 10-minute free calls" option usually fits. If your calls are short, this covers you.
• You make lots of long calls, for work or otherwise: Go for fully unlimited calling. Both sub-brands and cheap SIMs offer it.

One thing to watch: some brands' call packages assume you call from a dedicated app number. Before signing up, check whether that suits you, depending on whether you want to call normally from your phone's standard dialer or don't mind going through an app.

Match the ecosystem to the points you already collect

If the prices are close, let how well a brand fits the points ecosystem you already use make the final call. Rakuten Mobile tends to boost your point rate on Rakuten Ichiba purchases. The au brands (UQ/povo) link with Ponta and au PAY, the SoftBank brands (Y!mobile/LINEMO) with PayPay, and the docomo brands (ahamo/irumo) with d POINT. You may earn points on the phone bill itself or get higher rewards on shopping, which lowers your real cost. Combine this with how to think about point rewards, and you'll see differences the monthly price alone doesn't show. Check each official site for exact reward rates and conditions.

How MNP (switching while keeping your number) actually works

Many people never switch because it sounds like a hassle, but MNP has become much easier. You keep your phone number. It takes three steps.

1. Get an MNP reservation number (or skip this)Traditionally, your current company issues you a reservation number. But if both companies support MNP One-Stop (MNPワンストップ), you can skip this step entirely and do everything on the sign-up screen.
2. Sign up with the new companyHave your ID document and MNP reservation number (if needed) ready. This is where you choose eSIM or a physical SIM card (sent by mail).
3. Activate your lineWith a SIM card, you switch over after it arrives. With eSIM, you scan a QR code and can be up and running the same day, with no wait for the mail.

If you're in a hurry or would rather not leave home, eSIM is the way to go. It skips the few days of waiting for a physical card. For details, see how eSIM works and how to use it. For the finer points of the process, see MNP switching steps and things to watch for.

Switching pitfalls you won't find on the price list

More people actually trip up on small things they forgot to check during the transfer than on choosing the plan. Here are the common pitfalls to check in advance.

• Carrier email: Are you using an @docomo, @au or @softbank address for logins or as a contact address? If so, use the paid email carry-over service (メール持ち運び), or switch those accounts to a free email address such as Gmail before you move.
• Remaining phone installments: If you're still paying off your phone in installments, payments continue after switching. Check what happens to the remaining balance and how you'll pay once the line is canceled. For sorting out device costs, see ways to pay for your phone.
• Whether your current phone will work: Does your phone support the new network (especially if you're moving to a different one)? If it's SIM-locked, you may need to unlock it. If you're replacing the phone too, see choosing a SIM-free phone.
• Timing: Whether your final month is prorated or charged in full depends on the company. Whether the start or end of the month is better depends on each company's terms, so check first instead of rushing right before the billing cutoff.
• Two-factor and SMS verification: If you receive codes for banking apps or social media on your current number, MNP keeps your number so it's generally fine. But during the switchover, there may be a period when SMS doesn't arrive. Avoid switching right before anything important.

Don't switch once and forget it: a yearly check-up keeps you on track

Switching is a one-time task, but the best plan for you drifts over time. Companies keep launching new plans, and the way you use your phone changes too. If you work from home more and rely on Wi-Fi, you can cut your data. If you go out more, you may need a bigger plan. Make it a habit to compare last month's data usage with your current plan once a year, at an easy-to-remember time such as the new fiscal year or your birthday month, and you won't miss out.

Once your phone bill is sorted, applying the same approach to all your fixed costs pays off even more. Subscriptions, insurance, home internet: the things that are automatically charged every month are where the most room for savings is hiding. See also our complete guide to cutting fixed costs, when to replace your phone, PC or tablet for timing a new device, and the complete guide to saving in an era of price hikes.

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