The short answer for travellers
MobiFone 4G registration is a subscriber process: it assumes you already hold a MobiFone SIM registered to your passport or ID, and it changes the plan attached to that SIM. It is not the same thing as buying connectivity for a two-week holiday.
If that is what you actually need, skip to what to buy instead. If you are a resident, a long-stay visitor or someone who already has a MobiFone number, the steps below are the ones that matter.
What "đăng ký 4G MobiFone" actually means
Vietnamese mobile plans are sold as gói cước — a named package with a code, a data allowance, a validity period and sometimes a bonus. "Đăng ký" means subscribing to one of those packages on an existing number.
Three things have to be true before any registration will work:
- The SIM is active and registered. Since 2017 Vietnamese SIMs must be registered against a legal identity. A SIM bought informally and never registered cannot be subscribed to data packages.
- The number has enough balance for the package, or a linked payment method.
- You know the package code. MobiFone sells many; the code is what you type, not the marketing name.
How to register: the three routes
1. USSD code (fastest)
Dial the code for the package you want, then follow the confirmation SMS. MobiFone's own published codes follow the *090# family for data packages, with the specific code varying by package. If you do not know the code for the package you want, dial *090# and follow the menu, or check the current list in the My MobiFone app.
2. My MobiFone app
The app lists live packages with prices and validity, and lets you subscribe without remembering a code. This is the route to use if you are comparing options, because the app shows what is actually available on your number rather than what a forum post said in 2021.
3. At a MobiFone store or authorised dealer
Bring the passport or ID the SIM is registered to. Staff will subscribe you and can also fix a SIM that was never properly registered — which is the usual reason a registration attempt fails.
Why registration often fails
| Symptom | Usual cause | Fix |
|---|---|---|
| "Thuê bao không hợp lệ" | SIM not registered to a legal identity | Register at a MobiFone store with your passport |
| Package code rejected | Code retired or not available on your tariff | Check the live list in the My MobiFone app |
| Subscribed but no data | APN or handset setting | Reset APN to MobiFone defaults; toggle airplane mode |
| Balance deducted, no package | Wrong code dialled | Check the confirmation SMS before deleting it |
If you are a visitor, read this before registering anything
A tourist SIM bought at a Vietnamese airport or phone shop is usually already registered by the seller, and comes with a data package attached. That is why most arrivals never type a USSD code at all. The trade-off is the queue, the paperwork and the fact that the shop's package may not be the one you would have chosen.
For a trip of one to four weeks, a Vietnam eSIM removes the whole question. You install it before departure, it activates when it connects to a Vietnamese network, and there is no registration step because the plan is sold to you directly rather than attached to a locally registered SIM.
For a fuller comparison of the two routes, see Viettel, VinaPhone or MobiFone: how Vietnam's three networks compare.
What to buy instead
If you are travelling to Vietnam and the phrase "đăng ký 4G MobiFone" brought you here, the plan you want is a Vietnam eSIM, bought before you fly and installed on your phone.
- Buy it here: Vietnam eSIM plans — pick the data allowance and validity that match your trip length.
- Check your phone first: Vietnam eSIM for iPhone and Vietnam eSIM for Android cover compatibility and dual-SIM behaviour.
- Install it properly: Vietnam eSIM activation walks through installation, landing activation and first-connection fixes.
A quick decision table
| Your situation | Best option |
|---|---|
| 1–4 week holiday, modern phone | Vietnam eSIM, installed before departure |
| Staying 1–3 months, need a local number | Registered local SIM (MobiFone, Viettel or VinaPhone) |
| Already have a MobiFone number | Subscribe via the My MobiFone app |
| Two devices, one connection | eSIM plus hotspot — see Vietnam eSIM as a hotspot |
| Arriving late at night | eSIM; airport counters may be closed |
What the eSIM does and does not include
An eSIM gives you data. It does not give you a Vietnamese phone number for calls and SMS unless the specific plan says so — that is covered in Does a Vietnam eSIM come with a phone number?. If you need to make calls, apps like Zalo and WhatsApp handle most of it over data.
Network, validity and activation details come from the product record for the plan you choose, not from a general claim. Check the plan page before you buy.
If you have already bought a MobiFone package
Nothing here invalidates it. A registered MobiFone SIM with an active 4G package works normally, and you can use it alongside an eSIM if your phone supports dual-SIM. The two do not conflict; you simply choose which line carries data in your phone's settings.
If you have lost the link to an eSIM order, the help centre explains what to do — order links arrive by email and there is no public lookup page.