Guide to AT&T International Plans in Japan

Heading to Japan and wondering if your AT&T plan will work jut like it does back home?

AT&T offers two international options you can use in Japan:

• International Day Pass (IDP)
• Pay-per-use rates (pay as you go)

While these options do work abroad, they can get expensive depending on your current plan and the length of your trip.

In this article, we'll break down AT&T's international roaming options and introduce a more budget-friendly alternative: prepaid SIM and eSIM plans made for travelers in Japan.

Does AT&T Work in Japan?

Yes, AT&T customers can use their phones in Japan through international roaming. AT&T has a roaming partnership with NTT docomo, Japan's largest mobile carrier allowing you to connect to both 5G and 4G networks throughout the country.

Photo courtesy of AT&T

AT&T established its 5G roaming agreement with docomo in 2020, making it the first US carrier to offer 5G roaming in Japan.

On AT&T's coverage map, most of Japan appears in green, meaning you should get a signal in most places. 5G isn't guaranteed everywhere, but you should have 4G or at least 3G coverage, especially in cities and well-traveled areas.

AT&T International Plans for Japan

AT&T offers two ways to use your phone in Japan. Here's what you need ot know about each option.

Your Two Choices: IDP vs. Pay-Per-Use

How the 24-Hour Charging System Works

Here's the part that confuses most people: AT&T's International Day Pass charges you for reach 24-hour period you use your phone, not for each calendar day (AT&T, 2025b).

When does the clock start?
The first time you use data, send a text, or accept a phone call in Japan, your 24-hour period begins (Milne, 2025). That $12 charge covers you for the next 24 hours from that exact moment.

Example: You land in Tokyo at 3:00 PM on Monday and check your email. Your 24-hour period starts at 3:00 PM on Monday and runs until 3:00 PM on Tuesday. If you use your phone again at 4 PM Tuesday, you'll trigger another $12 charge for the next 24 hours.

Important warning: Background apps can trigger charges without you realizing it. Apps like email, weather, and social media often refresh automatically, which counts as "using data" and starts your 24-hour period. To avoid accidental charges, turn on airplane mode or disable data roaming when you don't want to use the service.

How the 24-Hour Charging System Works

Here's the part that confuses most people: AT&T's International Day Pass charges you for each 24-hour period you use your phone, not for each calendar day (AT&T, 2025b).

When does the clock start?
The first time you use data, send a text, or make or accept a phone call in Japan, your 24-hour period begins (Milne, 2025). That $12 charge covers you for the next 24 hours from that exact moment.

Example: You land in Tokyo at 3:00 PM on Monday and check your email. Your 24-hour period starts at 3:00 PM on Monday and runs until 3:00 PM on Tuesday. If you use your phone again at 4 PM Tuesday, you'll trigger another $12 charge for the next 24 hours.

Important warning: Background apps can trigger charges without you realizing it. Apps like email, weather, and social media often refresh automatically, which counts as "using data" and starts your 24-hour period. To avoid accidental charges, turn on airplane mode or disable data roaming when you don't want to use the service.

The 10-Day Cap (And Why It Can Be Misleading)

AT&T advertises that you'll "never pay for more than 10 days" with the International Day Pass. Here's what that actually means—and why it might cost more than you expect.

The truth about the 10-day cap:

• You're charged a maximum of 10 times per billing cycle, not per trip.
• Maximum cost: $120 per line per billing cycle.
• The catch: If your trip crosses into a new billing cycle, the counter resets to zero

Real-world scenario:
Let's say your AT&T billing cycle runs from the 1st to the end of each month. You're traveling to Japan from April 25 to May 8 (14 days total).

• April 25–30: 6 days of use → Charged $12 × 6 = $72 (counted in April's billing cycle)
• May 1–8: 8 days of use → Charged $12 × 8 = $96 (counted in May's billing cycle)

Total IDP charges: $168 for your 14-day trip, even though AT&T says there's a "$120 cap."

This happens because each billing cycle has its own separate 10-day limit. The cap doesn't carry over from one cycle to the next, so trips that span two billing cycles can cost significantly more.

Money-saving tip: Before you book your trip, check when your AT&T billing cycle resets. If possible, plan your travel to fall entirely within one billing cycle to take advantage of the 10-day cap.

Quick Data Reference: How Many GB Do You Need for a 5-Day Stay?

Wondering how much data you'll actually use in Japan? Here's a realistic breakdown:

If you're on an AT&T unlimited plan with the IDP, you don't need to worry about these numbers. But if your plan has a data cap (like 75 GB before throttling), be aware that your domestic data limits still apply when you're abroad.

Why Pay-Per-Use Is Not Such a Good Idea

Without the International Day Pass, you'll be charged $2.05 per MB of data. Here's what that means in real money:

• 1 GB of data = $2,099 (1,024 MB × $2.05)
• 15 minutes of Spotify = ~$154
• One 10-minute YouTube video = ~$144
• 5-minute video call = ~$72
• 1 text message = $0.50
• 1 picture/video message = $1.30

Unless you're only planning to send a couple of texts, pay-per-use rates can quickly drain your wallet. We strongly recommend against using this option.

What About AT&T Prepaid?

Important note: The International Day Pass is only available for AT&T postpaid plans (AT&T, 2025e). If you have AT&T Prepaid, you have different international options (like the $35/7-day Travel Add-On with 5 GB of data). This article focuses on postpaid international roaming.

Instead of paying for expensive international roaming plans (like AT&T’s), skip the hassle and go with a local eSIM/SIM!

• You likely won’t need your U.S. number while you’re in Japan.
• You’ll save a ton on roaming fees.
• Sakura Mobile’s 5G unlimited data eSIM gives you full coverage (on the au network).
• Perfect for maps, social media, and streaming.
• No FUP = no throttling, truly unlimited data with no slowdowns.

Is AT&T Worth It in Japan?

Now for the big question: should you actually use AT&T's international plans in Japan?

The real cost breakdown:
Your monthly AT&T bill includes your domestic plan fee PLUS the IDP charges. Current AT&T unlimited plans range from $65.99/month (Unlimited Starter SL) to $85.99/month (Unlimited Premium PL) for a single line.

Here's what a typical trip costs:

Even with the cheapest unlimited plan, a 7-day trip will add around $150 to your monthly bill.

How Sakura Mobile compares:
Many providers sell prepaid eSIM/SIM cards for Japan that cost about half the price of AT&T's plans. Here's how Sakura Mobile's unlimited data plans stack up:

(USD conversion based on exchange rate of 142.69 yen per dollar as of April 2025. Tax included.)

Sakura Mobile's 5G truly unlimited eSIM offers unlimited 5G data with no daily caps and no throttling for 5,500 yen for 7 days.

The bottom line: AT&T's International Day Pass is convenient because you keep your US number active and don't need to swap SIM cards. But that convenience comes at a cost that is double or even triple the price of a local SIM or eSIM.

Critical Things to Watch Out For

If you decide to use AT&T's international plans, be aware of several potential pitfalls that can lead to unexpected charges. Here's what you absolutely need to know.

Avoiding Double Billing: The Most Important Setup Step

This is the single most common (and costly) mistake travelers make.

If you're using a local SIM or eSIM in Japan alongside your AT&T line, you need to set things up correctly, or you'll get charged by both services.

What happens if you forget:
Modern phones support dual SIM functionality (a physical SIM plus an eSIM, or two eSIMs). Your phone might automatically switch between your AT&T line and your travel eSIM without you realizing it.

The result is you get hit with AT&T's $12/day IDP charge AND pay for your travel eSIM. Some travelers have reported being charged hundreds of dollars this way.

How to prevent double-billing:
Follow these steps before you leave for Japan:

Step 1: Turn OFF Data Roaming for Your AT&T Line
This is the most important setting.

For iPhone:

• Go to Settings → Cellular→Cellular Data Option
• Tap on your AT&T line
• Turn OFF "Data Roaming"

For Android:

• Go to Settings → Connections → Mobile Networks
• Select your AT&T SIM
• Turn OFF "Data Roaming"

Step 2: Set Your Travel SIM/eSIM as Default for Data

• For iPhone:Settings → Cellular → Cellular Data → Select your travel eSIM
• For Android:Settings → Connections → SIM Manager → Set travel eSIM as preferred

Step 3: Turn ON Data Roaming for Your International Roaming Plan (IDP)
This sounds backward, but your travel eSIM needs data roaming enabled to connect to local networks. Since it's prepaid, there's no risk of extra charges. For Sakura Mobile eSIM customers, it’s vital that data roaming be turned off so as not to incur double charges.

Step 4 (Optional): Keep AT&T Active for Texts Only
You can keep your AT&T line on to receive SMS verification codes (useful for banking apps), but make sure data roaming stays OFF. Please note that you'll be charged for any outgoing calls made. Please keep in mind that this is for eSIMs only. If you are using a physical SIM card, you will not be able to use your cellphone number from the US until you switch back.

Emergency option: If you're unsure, put your phone in airplane mode and manually turn WiFi back on. This prevents all cellular charges while still letting you use WiFi.

Tethering and Hotspot

Whether you can use tethering (mobile hotspot) with AT&T's IDP depends on your specific domestic plan. If your plan includes hotspot data at home, it should work abroad—but double-check with AT&T before you travel. Some plans limit hotspot usage even if they offer "unlimited" data.

Who Should Use AT&T in Japan (and Who Shouldn't)?

Let's make this simple. Here's who benefits from AT&T's international plans—and who would be better off with a local SIM or eSIM.

Use AT&T if:

• You need your US phone number to be active for work or family emergenciesIf you're traveling for business or need to stay reachable on your US line, keeping AT&T active makes sense.
• You're visiting multiple countries and don't want to swap SIMsThe IDP works in over 210 countries, making it convenient for multi-country trips.
• You don't mind paying extra for convenienceIf the added cost doesn't bother you and you value the simplicity of not having to change SIM cards, go for it.

Skip AT&T if:

• You want to save moneyLocal SIMs and eSIMs cost half (or less) than AT&T's IDP.
• You don't need to receive calls on your US numberIf you're fine using WhatsApp, LINE, or other apps to stay in touch, you don't need AT&T active.
• You're not comfortable managing dual-SIM settingsIf the idea of turning off data roaming and avoiding double-billing sounds confusing, it's safer to use a local SIM and leave your AT&T line at home.
• Your phone is carrier-lockedLocked phones can't use local SIMs. You'd need to unlock it first or rent a Pocket WiFi device instead.

Related Articles

• Verizon in Japan: Comparing Plans and Cheaper SIM Options
• Guide to T-Mobile’s Japan Roaming Plans

Why Sakura Mobile Is the Safer, Simpler Choice

If you've read this far, you probably realize that AT&T's international plans come with a lot of "ifs," "buts," and potential surprises. Here's why many travelers choose Sakura Mobile's travel SIM and eSIM plans instead.

No Risk of Surprise Charges

With Sakura Mobile, you pay upfront—that's it. No daily fees that add up. No billing cycle confusion. No accidental double charges because you forgot to turn off a setting.

You know exactly what you're paying before you land in Japan.

Truly Unlimited Data (Really)

Sakura Mobile's 5G unlimited eSIM/SIM card offers truly unlimited high-speed data with no daily caps and no throttling. That means you can:

• Stream videos without worry
• Use Google Maps all day
• Video call friends and family back home
• Share your trip on social media as much as you want

No "3 GB per day" limits. No slowdowns after hitting a cap. Just fast, reliable 5G on Japan's au network.

If your phone isn't eSIM compatible, Sakura Mobile also offers a 4G unlimited physical SIM starting at just 4,950 yen (~$35) for 7 days, with up to 2 GB of high-speed data per day and unlimited low-speed data after that.

Easy Setup with Full English Support

Sakura Mobile specializes in helping English-speaking travelers. You get:

• Clear setup instructions in English
• Email and phone support if you run into issues
• Instant eSIM activation via QR code (takes about 5 minutes)
• Airport pickup for physical SIM cards at major airports

And here's something unique: if your phone turns out to be incompatible with a SIM or eSIM (although this is rare), Sakura Mobile will immediately upgrade you to a pocket WiFi device at no extra charge with compatibility insurance.

Coverage Across All of Japan

Sakura Mobile operates on both the au and docomo networks. And since AT&T roams on docomo in Japan, you get the same coverage, but at a fraction of the price.

Independent speed tests show Sakura Mobile averaging 449 Mbps download speeds, putting it near the top of Japan's eSIM providers.

For comparing short-term SIM/eSIM plans, check out the following article about comparing limited and unlimited plans!

Japan Prepaid SIM Data: Comparing Limited vs. Unlimited Plans

Data-Saving Tips (If You Choose a Fixed-Data Plan)

If you opt for one of Sakura Mobile's fixed-data plans instead of unlimited, here are quick ways to make your data last:

• Download offline maps before you leave (Google Maps, Apple Maps)
• Turn off auto-play videos on Facebook, Instagram, and Twitter
• Download music and podcasts on WiFi instead of streaming
• Use hotel, cafe, and convenience store WiFi when available (most 7-Elevens and Family Marts offer free WiFi)
• Disable background app refresh for apps you don't need constantly updating

But honestly? With Sakura Mobile's truly unlimited 5G eSIM plans starting at just 4,400 yen (~$31) for 4 days, you might not need to worry about data management at all.

🔎 Don’t get stuck with the wrong carrier while traveling in Japan.
Learn about what you should know about Japan’s Mobile Networks here!
➡️➡️ Japan Mobile Network Guide for Travelers and Tourists

Check This Before Your Trip

Before you head to Japan—whether you're using AT&T's international plans or buying a local SIM/eSIM—there's one critical thing you need to verify.

Is Your Phone Unlocked?

If you plan to use a local SIM or eSIM, your phone must be unlocked (also known as SIM-free or carrier-unlocked). AT&T-locked phones will only work with AT&T SIM cards.

How to check if your phone is unlocked:

For iPhone:

• Go to Settings → General → About
• Scroll down to "Carrier Lock"
• If it says "No SIM restrictions," your phone is unlocked

For Android (Samsung):

• Go to Settings → Connections → Mobile Networks → Network Operators → Switch "Select Automatically" off
• Search for available networks
• If multiple carriers appear, your phone is unlocked

If your phone is locked:

You'll need to unlock it through AT&T before you can use a local SIM. AT&T's unlock requirements include:

• Your device must have been purchased at least 60 days ago
• Your phone must be paid off in full
• No outstanding balance on your account
• Device not reported lost or stolen

You can submit an unlock request at att.com/deviceunlock. Most requests are processed within 24–48 hours.

Alternative if your phone is locked:
If you can't or don't want to unlock your phone, you can rent a pocket WiFi device from Sakura Mobile. Pocket WiFi works with any phone—locked or unlocked—and multiple people can connect to the same device.

Device Compatibility

Most modern smartphones work in Japan, but older or regional models might not support the right frequency bands. Sakura Mobile offers a compatibility checker on their website. If your phone turns out to be incompatible, they'll upgrade you to a Pocket WiFi at no extra charge if you have compatibility insurance.

FAQ

Enjoy Your Trip to Japan!

AT&T's International Day Pass can be a suitable option for short trips to Japan if you need to keep your US number active and are comfortable managing the settings to avoid unexpected charges. But between the daily fees, the billing cycle confusion, and the risk of double-billing with dual SIM setups, it's easy to end up paying more than you expected.

That's why many travelers choose a simpler option: Sakura Mobile's prepaid SIM and eSIM plans.

With Sakura Mobile, you get:

• Truly unlimited 5G data – No daily caps, no throttling, no surprises
• Half the cost of AT&T's International Day Pass
• No risk of double-billing – Pay once upfront, that's it
• Full English support – From a team that understands Japan's networks
• Easy setup – Instant eSIM activation via QR code, or airport pickup for physical SIMs

Pre-order your Sakura Mobile Travel SIM/eSIM now and stay connected from the moment you land in Japan.

👉 Get Your Sakura Mobile eSIM Here

👉 Get Your Sakura Mobile Physical SIM Here

Have a great trip to Japan! 🌸