Budget SIM or Major Carrier? Comparing Actual Costs for Vietnamese People in Japan

"Hey brother, I heard Docomo SIMs have the strongest signal, but they're expensive — is it worth it?" — this is almost the question we receive most from newcomers. The honest answer is: it depends on who you are. This article won't shout "cheap SIMs forever" or "big brands are worth every penny," but will break down every cost so you can see for yourself which option fits your budget and habits.

1. Market Overview: Three Tiers of Carriers in Japan

• Tier 1 — The Big Three Carriers (MNO): Docomo, au (KDDI), SoftBank. They own cell towers, physical stores everywhere, full service — and the highest prices, usually ¥5,000–8,000/month for comfortable data plans with calls included.
• Tier 2 — Budget Sub-brands: ahamo (Docomo), UQ mobile/povo (au), Y!mobile/LINEMO (SoftBank). They share the parent company's network, cost around ¥2,000–3,000/month, but registration is mostly online and almost strictly requires a credit card.
• Tier 3 — Budget SIMs (MVNO / kakuyasu SIM): companies that lease network coverage from the big three and sell low-cost plans, starting from around ¥1,000/month. This is the segment most Vietnamese newcomers choose — including SIM plans from HD TELECOM.

2. Head-to-Head Comparison of What You Care About

3. Hidden Costs Ads Don't Mention Out Loud

At Major Carriers

• Initial setup fee around ¥3,000 when signing up at a store.
• "First 6 months promo" prices: many cheap plans only last for the first half year, then automatically increase — read the fine print carefully.
• Installment payments disguised as "¥0 phone": "free" phones are actually deducted gradually from your bill; leave early and you must pay off the balance.
• Auto-renewing add-on services: phone insurance, ringback tones, video services... staff often preset "first month free," and if you forget to cancel, you lose ¥500–1,500/month.

At Budget SIM Providers

• Peak-hour speeds: this is the real "cost" — paying less means accepting slower speeds during crowded times. For those mainly texting or checking maps, it's barely noticeable; for those streaming movies right during lunch break, it is.
• No physical stores everywhere: damaged SIMs or lost phones must be handled online — so choose a provider with support channels you feel comfortable using (for Vietnamese users, that means Vietnamese support via Zalo, Messenger, LINE).

4. Doing the Math for a 2-Year Period

Suppose you are a technical intern in Japan for 3 years, needing 20GB/month:

• Major carrier option (standard plan at ¥6,000/month): 24 months × ¥6,000 = ¥144,000.
• Sub-brand option (¥2,970/month): 24 months ≈ ¥71,000 — but requires a Japanese credit card right from the start, something newcomers don't have yet.
• Budget SIM option (¥2,000/month): 24 months = ¥48,000, sign-up without needing a credit card.

The difference between the most expensive and cheapest option is nearly ¥100,000 over 2 years — equivalent to a round-trip flight back to Vietnam plus gifts. That is why the majority of the Vietnamese community chooses Tier 3, unless they have special needs.

5. When is it WORTH paying extra for a major carrier?

To be fair, major carriers are right for you if:

1. Your job relies heavily on peak-hour internet: food delivery drivers, continuous online meetings, livestream selling — a few seconds of delay means lost money.
2. You need to buy the latest iPhone on installment at a good rate bundled with a contract and plan to stay long term.
3. You live in mountainous regions or islands where only the native carrier network has good coverage (rare, but it happens).
4. Your whole family uses it together and can take advantage of group discounts + home internet bundling — bringing the cost per person down close to budget SIM rates.

If you don't fall into these four categories, the monthly price difference is mostly just buying brand peace of mind.

6. How to Smartly Choose a Budget SIM?

1. Check the underlying network: MVNOs run on Docomo/au/SoftBank networks — any base network covers cities well; in rural areas, ask local colleagues which network gets better signal.
2. Check payment methods: newcomers without a Japanese credit card must choose providers accepting bank transfers, convenience store payments, or cash on delivery (COD).
3. Check plan change policies: does changing data allowance next month cost extra? Flexibility is a more important criterion than just the absolute cheapest price.
4. Check support channels: when trouble hits at 9 PM, who do you message? In what language? How fast do they reply?
5. Read cancellation terms: a good plan is one that lets you leave easily — no penalties, no 12-month lock-in.

7. Frequently Asked Questions

Do budget SIMs block video calls back to Vietnam?

No. Zalo, Messenger, LINE, and FaceTime run on data equally across all carriers. Call quality depends on your network speed at the time of the call.

If I'm using a major carrier, can I switch to a budget SIM and keep my number?

Yes — the MNP (Mobile Number Portability) process applies to 070/080/090 numbers. Request an MNP code from your old carrier (most provide it online for free now), give it to your new carrier when signing up, and you're done; your number stays with you.

I often go back to Vietnam for 1–2 months; should I cancel my Japanese SIM and buy a new one later?

For SIMs with no contract obligations, compare two numbers: the cost to maintain the lowest plan while away versus the hassle of re-registering (plus the risk of losing your phone number). Usually, keeping a small plan worth a few thousand yen is well worth it, especially when your phone number is tied to bank accounts and e-wallets in Japan.

Conclusion

Don't ask "Which SIM is best?" — ask "Which SIM suits me for the next 1–2 years?". Newcomers who don't have a credit card and need to save money: budget SIMs with flexible payment options are almost the default answer. Those who are settled, using it with family, and need strong network speed at all hours: consider major carriers with family discounts. If you want someone to calculate this for you in Vietnamese tailored to your exact situation, the HD TELECOM team is always ready — free consultation, no pressure to buy.