Before you start

Your original passport (registration is mandatory and tied to it)
A Vietnamese address or hotel where you're staying
An unlocked phone (or eKYC at the store for an eSIM)

Step-by-step

1
Pick a carrier
Viettel has the widest coverage (best outside cities), Mobifone and Vinaphone are strong in HCMC. All three sell cheap high-data prepaid plans; differences are mostly coverage and shop convenience.
In personWho: You——
2
Buy at an official store or airport kiosk — not a street stall
Go to a branded Viettel/Mobifone/Vinaphone store or an official airport counter. Staff scan your passport and register the line under your name (eKYC). Avoid random shops selling pre-activated SIMs registered to someone else.
In personWho: You~15–30 minutesSIM + plan from ~VND 150,000
3
Confirm the line is registered to YOU
Make sure the SIM is registered under your own passport, not pre-activated. An unregistered or falsely registered line can be blocked by the network with no notice — and you can't use it for bank OTPs.
In personWho: YouAt purchase—
4
Top up a data plan
Add a monthly data package via the carrier app, a top-up card, or at the store. Daily-GB tourist bundles run a few dollars; locals use cheaper monthly packs once registered.
Mobile appWho: YouMinutes~US$6–10/mo typical

Documents you’ll need

Original passport (mandatory for registration)
Vietnamese address or hotel details
Unlocked phone or eSIM-capable device

Things most newcomers don’t know

Registration is mandatory and tied to your passport.

Vietnam requires carriers to verify and record a foreigner's passport when issuing a SIM (Decree 49/2017, reinforced by the Telecom Law). If a vendor doesn't ask for your passport, the line is registered to someone else.

Source: official (Decree 49/2017 / Telecom Law)

A pre-activated street SIM can be cut off without warning.

Authorities deactivated roughly 12 million falsely registered SIMs; 'ghost' SIMs sold ready-to-use are exactly the ones that get blocked. Buy at an official store so the line is yours and stays on.

Source: news reporting + carrier guidance

You need a registered line before you can bank.

Vietnamese banks send OTPs to a local number and many tie onboarding to it — so a properly registered SIM is a prerequisite, not an afterthought.

Source: provider consensus

Data is genuinely cheap once you're set up.

High-data prepaid plans cost only a few dollars a month, so there's little reason to ration mobile data — just make sure the underlying line is registered.

Source: provider guides

Common mistakes to avoid

Buying a pre-activated SIM from a street vendor (registered to a stranger, can be blocked)
Not bringing your passport — official stores can't register the line without it
Assuming you can open a bank account before you have a working local number

Make it your personal checklist

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