The classic backpacker loop runs from Bangkok to Chiang Mai, down the Mekong by slow boat to Luang Prabang, on to Vietnam's mountains and coast, and ends at the temples of Angkor in Cambodia. Some borders are crossed by bus or boat, others by plane, and each brings new networks. None of the four is in the EU's Roam Like at Home area, and a plan for one country does not cover the next.
This guide to an eSIM for Southeast Asia covers the Best Asia plan, when country plans make more sense, land borders, and where the signal fades.
Key facts for a Thailand, Laos, Vietnam and Cambodia loop
- One plan for the route: the Best Asia plan covers all four among 17 destinations; the Asia plan covers all four among 26
- EU roaming: none of the four countries is covered by Roam Like at Home
- Local networks: AIS, TrueMove H and dtac in Thailand; Wintel, VinaPhone and MobiFone in Vietnam; Metfone, Cellcard and Smart in Cambodia; Lao Telecom, Unitel and ETL in Laos (depending on the plan)
- Emergency numbers: different in each country; Thailand's Tourist Police answer on 1155
- Embassies: in Bangkok, Hanoi, Phnom Penh and Vientiane
One eSIM for Thailand, Vietnam, Cambodia and Laos
The Best Asia plan covers all four countries on one eSIM, installed once at home for the whole loop, plus Malaysia, Singapore and Indonesia, among others. Country plans cover one country each, so you install one per country and switch your data line at every border.
Crossing land borders
Near a land border, a phone can connect to the neighbouring country's network before you cross. With Best Asia or Asia, that network is covered, and after the border the phone should find a local network by itself while data roaming is on for the eSIM; if not, choose one manually.
With a single-country plan, the neighbour's network is not covered: choose your current country's network manually near the border, and switch your data line to the next country's plan once across.
Before planning an overland leg, read the travel-safety pages below on border areas.
Islands, rivers and mountain roads
Coverage is good in the main cities and towns but fades on the water and in the hills. On the Mekong slow boat the signal drops for long stretches; on Thai island speedboats, remote beaches and dive trips it can disappear; on Ha Long Bay it weakens among the outer islands. The mountain loops around Pai and Mae Hong Son in Thailand and Ha Giang in Vietnam have long weak stretches.
Download offline maps, boat tickets and your next address before you leave the pier or the last town.
Which plan fits your trip
For the full loop, Telcomia's Best Asia plan is the simple choice: one eSIM for all four countries. The Asia plan covers them too; compare the two if your route goes further. A country plan, such as Vietnam, fits a trip spent in one country, but it does not cover the neighbours.
Open the plan details before you buy: they show the duration, the data, whether you can share the connection with other devices, and the Activation line, which tells you what starts the plan's validity.
Before you leave
- Read the Activation line in the plan details, then install the eSIM at home on Wi-Fi.
- Set the eSIM as your mobile data line, with data roaming on for the eSIM and off for your home line.
- Download offline maps for the Mekong, the islands and the mountain loops.
- Move any Telegram groups to another app before Vietnam: since mid-2025, operators there have been ordered to block it.
- Keep the eSIM installed until the trip is over: some eSIMs can be installed only once.
Consular protection: four countries, four sets of numbers
- In Thailand, 191 is the police, 1669 an ambulance and 199 the fire service; the Tourist Police answer on 1155.
- In Vietnam, 113 is the police, 114 the fire service and 115 an ambulance. In Cambodia, 117 is the police, 118 the fire service and 119 an ambulance. In Laos, 1191 is the police, 1195 an ambulance and 1190 the fire service.
- Embassies are in Bangkok, Hanoi, Phnom Penh and Vientiane, with consulates in Chiang Mai for some countries. The Telcomia app shows which mission is responsible for you, with address and phone.
- If you are an EU citizen and your country has no embassy or consulate in Thailand, Vietnam, Cambodia or Laos, the embassy of any other EU country must help you on the same terms as its own nationals (Article 23 of the Treaty on the Functioning of the EU).
- Emergency phrases in Thai and Vietnamese are ready to show on screen in the app.
Questions travellers ask about the Southeast Asia loop
Is there one eSIM for Thailand, Vietnam, Cambodia and Laos?
Yes. The Best Asia plan covers all four on a single eSIM, and so does the Asia plan.
Does the eSIM switch when I cross a land border?
With Best Asia or Asia, yes: the phone moves to a network in the new country, which the plan covers. A single-country plan does not cover the next country.
Best Asia or country plans?
Best Asia, for a loop through two or more of the four countries. A country plan suits a trip that stays in one.
Which tourist police numbers should I save?
In Thailand, 1155 reaches the Tourist Police around the clock, in several languages, and Vientiane in Laos has a tourist police office. Elsewhere, save the police numbers, and if the operator speaks only the local language, ask your hotel to call for you.
The short version
One Best Asia plan covers the whole loop on one eSIM; a country plan suits a trip in one country. Install it at home, download maps before boat trips and mountain roads, and save 1155.
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