Most guides about mobile data in Thailand tell you the same thing: coverage is great, buy any eSIM, you will be fine. That is broadly true if you never leave Bangkok. The moment your trip includes islands, national parks, or the north, it stops being true, and the difference comes down to one thing almost no guide explains clearly: which Thai network your eSIM actually connects to.
This guide covers the two networks that run Thailand today, which one matters for your specific itinerary, what coverage is really like across the places tourists actually go, and how to arrive already connected, including one free government form you now have to complete before you fly.
Thailand has two networks now, not three
For years, Thailand had three big operators: AIS, TrueMove H, and DTAC. That changed in 2023, when TrueMove H and DTAC merged into a single company, True Corporation. You will still see the DTAC name on some tourist SIMs and older plans, but underneath, those customers now share the same towers under True's "One Network" integration. In practice, Thailand is now a two-horse race between AIS and True.
They are not identical, and the gap is exactly where travellers get caught out.
AIS is the largest operator, with roughly 46 percent of the market and the widest geographic footprint. It has the most rural towers and the strongest signal on islands, in the mountains, and along remote routes. In independent network testing by Opensignal, AIS has taken the outright coverage award in Thailand. If your itinerary leaves the cities, AIS is the network you want to be on.
True Corporation (the merged True and DTAC) holds around a third of the market and performs excellently in Bangkok and the major tourist cities, often with very fast 5G. Its weaker point is remote islands and outer provinces, where the two legacy networks are still being fully integrated.
There is also NT (National Telecom), a small government-owned operator. It has no meaningful presence in the travel eSIM world, so you can safely ignore it.
Why "which network" matters more than "which brand"
Here is the practical catch. When you buy a Thailand eSIM, you are not really buying "an eSIM for Thailand." You are buying access to one specific local network. Some providers route you onto True and DTAC, some onto AIS, and a few give you access to more than one.
In Bangkok, Phuket, Pattaya, Chiang Mai, and Koh Samui, this barely matters. Both networks are strong and you will not notice the difference for maps, messaging, and streaming. But if your trip includes smaller islands, Khao Sok, Pai, or anywhere genuinely rural, an eSIM that only routes to True can leave you with a weaker signal exactly where you needed it most, while an AIS-based plan holds up.
So before you buy, check the plan's supported network. If your trip is city-only, take the best value. If you are island hopping or heading north, prioritise a plan that includes AIS.
Coverage across the places you will actually go
Bangkok and major cities. Near-total 4G and widespread 5G on both networks. You get signal on the BTS Skytrain, in the MRT underground, in malls, and across all the main tourist areas. Both airports, Suvarnabhumi and Don Mueang, have strong coverage, so your eSIM can connect the moment you land.
Chiang Mai and the north. Excellent in the city itself, including the old town, Nimman, and the main temples. It thins out in the surrounding mountains and on routes toward Pai and Mae Hong Son, where AIS tends to hold a signal longer.
The islands. The big tourist islands (Phuket, Koh Samui, Koh Phangan, Koh Tao, Koh Lanta, Phi Phi) have solid 4G, often 5G, in their populated areas and beaches. It is the smaller and more remote islands where it gets patchy: places like Koh Lipe, Koh Kood, and Koh Mak have basic coverage with genuine dead zones, and the Similan and Surin islands have little to none. Ferries between islands can also drop out mid-crossing. The fix is simple and worth doing regardless of network: download offline Google Maps for your area before you leave the mainland. If your trip is built around island hopping, our Thailand island-hopping guide covers the routes and connectivity in detail.
National parks. Expect coverage near entrances, visitor areas, and accommodation, and expect it to disappear on deep trails. In Khao Sok, for example, there is signal around the lake bungalows but not in the jungle interior.
Be online before you clear immigration: the TDAC
This is the part most connectivity guides miss entirely, and it now affects every visitor. Since May 2025, Thailand has scrapped the old paper arrival card and replaced it with the Thailand Digital Arrival Card (TDAC), an online form that every foreign national must complete before entering by air, land, or sea.
A few things worth knowing:
- You submit it online within 72 hours (3 days) before your arrival date. The system will not accept it earlier.
- It is completely free. The only official site is tdac.immigration.go.th. Any site charging a fee for it is not official.
- You get a QR code by email that you show at immigration. Save it offline as well as keeping it in your inbox.
- Kiosks exist at the major airports if you miss the window, but queues in peak season are long, so doing it in advance is far easier.
The connectivity angle is straightforward. This is one more reason to have your data sorted before you travel, because keeping your QR code and details to hand is much easier when your phone is already online.
Tourist SIM or eSIM?
Thailand is one of the countries where local tourist SIMs are genuinely competitive, so it is worth an honest comparison.
Local tourist SIMs from AIS, True, and DTAC are sold at both airports and in convenience stores. AIS "Lucky Tourist" style packages, for example, have started at around 499 baht for roughly 8 days of unlimited data at the time of writing, and they usually bundle a local number and some call credit. The airport versions are convenient but marked up. The same or better value is often found at a 7-Eleven or an operator shop in town. You will need your passport to register a physical SIM.
An eSIM trades that in-person step for convenience. You install it at home over Wi-Fi, then it activates when you land, with no counter visit and no swapping out your home SIM. For solo travellers and couples this is usually the easier choice. Groups of three or more, or anyone who needs a local phone number for bookings, sometimes still prefer a physical tourist SIM.
One thing Thailand does not throw at you: the kind of device registration hurdles some neighbouring countries impose on foreign phones. An unlocked, eSIM-capable phone will simply work.
How much data do you actually need?
A rough guide for a week, assuming normal tourist use:
- Light use (maps, messaging, the odd search): around 1 to 3 GB.
- Normal use (all of the above plus social media, photos, and some video): around 5 to 10 GB.
- Heavy use (lots of streaming, video calls, tethering a laptop, remote work): 15 GB or more, or an unlimited plan.
Two Thailand-specific notes. Grab, the ride-hailing app, is close to essential and runs entirely on your data, though it is light, around 50 MB a day. And LINE is the default messaging app in Thailand, so if you are coordinating with local guides, hotels, or tour operators, you will want it working from the moment you arrive.
The short version
- Thailand runs on two networks now: AIS and True. AIS wins outside the cities.
- City-only trip: any decent eSIM is fine. Islands or the north: choose a plan that includes AIS.
- Coverage is excellent in cities and on the main islands, and patchy on remote islands and deep in national parks. Download offline maps before ferries and treks.
- Complete the free TDAC online within 3 days of arrival, only at tdac.immigration.go.th.
- Sort your data before you fly, whether that is an eSIM installed at home or a tourist SIM you pick up on arrival.
Ready to get connected? Compare Thailand eSIM plans before you fly.
This guide is for general information only and does not constitute legal, immigration, or telecoms advice. Networks, coverage, prices, plans, and entry requirements change regularly. Verify current details with the relevant provider and official Thai government sources before you travel.
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