What ST90K is
ST90K is one of the plan codes Vietnamese carriers use to sell prepaid bundles to their own subscribers. The letters and numbers are a catalogue reference: the carrier publishes it, the subscriber dials a short code or opens the carrier app, and the bundle is attached to a Vietnamese SIM that is already registered to a Vietnamese identity document.
That last part is the whole problem for a visitor. Prepaid SIM registration in Vietnam requires the subscriber's own identity details, and the plans in the catalogue are written for people who live with that SIM in their phone every day. A plan code like ST90K is not a product you can walk into a shop and buy as a foreigner on a two-week trip.
If you found this page by searching the code, you are almost certainly in one of two situations: you are a Vietnamese subscriber comparing bundles, or you are a traveller who saw the code somewhere and wondered whether it is the thing you should buy at the airport. This page answers the second question first, because that is the one that costs money when it goes wrong.
Why travellers should not chase a carrier plan code
A Vietnamese prepaid plan is built around a Vietnamese SIM. To use one you need to buy the SIM, register it, top it up, activate the bundle, and then keep track of a validity window that runs on Vietnamese carrier rules. On a short trip, that is a lot of admin for a result you can get before you board.
There is also the language problem. Plan catalogues are published in Vietnamese, the short codes are in Vietnamese, and the customer support line is in Vietnamese. If the bundle does not activate, you are troubleshooting in a language you probably do not speak, on the first day of your holiday.
The practical alternative is an eSIM. It installs before you fly, activates when you land, and needs no shop, no registration queue and no Vietnamese phone number. You keep your own number for WhatsApp and banking, and you get local data on the second line.
What ST90K-style plans are actually for
Carrier plan codes exist because Vietnamese subscribers genuinely need them. A domestic user wants a monthly data allowance, maybe some voice minutes, maybe free access to a specific app, and they want it renewing automatically. The codes are the carrier's way of packaging that.
As a visitor, your needs are different in almost every dimension:
| What you need | Domestic plan (ST90K-type) | Travel eSIM |
|---|---|---|
| Buy before you fly | No | Yes |
| Vietnamese ID registration | Required | Not required |
| Activation on landing | Manual, in Vietnamese | Automatic |
| Validity matched to a short trip | Rarely | Yes, by day count |
| Keep your home number active | Only with dual-SIM juggling | Yes, dual-SIM by design |
| Support in English | Usually not | Yes, via the help centre |
| Top-up mid-trip | Carrier app, in Vietnamese | Online, in your language |
That table is the honest comparison. A domestic plan can be cheaper per gigabyte if you are staying for months and have the paperwork. For a holiday, it is the wrong tool.
What to buy instead
For a trip to Vietnam, buy a Vietnam eSIM before departure. The store page lays out the plans by data allowance and validity, so you can match the purchase to the length of your trip rather than guessing at a carrier code.
A few things worth knowing before you choose:
- Match validity to your trip, not to your data habit. A ten-day trip does not need a thirty-day plan, and a thirty-day plan does not help a ten-day trip.
- Check your phone supports eSIM first. Most recent iPhones and most recent Android flagships do. If you are unsure, the Vietnam eSIM for Android and Vietnam eSIM for iPhone guides walk through compatibility and dual-SIM setup.
- Decide whether you need a phone number. If you only need data for maps, messaging and bookings, a data-only eSIM is enough. If you need to make or receive calls on a Vietnamese number, read Does a Vietnam eSIM come with a phone number? before you buy.
- Install before you fly, activate on landing. The activation guide covers the install steps and the common first-connection problems.
If you are still comparing the shape of the market, the Vietnam eSIM price guide explains what moves the price, and Pocket Wi-Fi or eSIM for your trip to Vietnam? covers the alternative if you were considering a pocket router instead.
If you are a Vietnamese subscriber reading this
ST90K is a catalogue entry, and the catalogue is where the plan's own terms live. The plan page quotes the code exactly as the carrier sells it, along with the network, validity and activation details from the product record. That is the page to read if you are comparing bundles for your own SIM.
This site does not run its own carrier top-up inventory. Catalogue pages are informational, and where a plan is linked, the link goes to the matching plan page rather than to a checkout.
The short version
ST90K is a domestic carrier plan code. It is not a tourist product, it is not sold to visitors, and it is not what you should be looking for on arrival. Travellers should buy a Vietnam eSIM before flying, install it at home, and land with data already working.