Thailand: SIM, eSIM, and wifi

Quick answer

Buy an eSIM before you leave, or buy a tourist SIM at the airport when you land. Do not leave the phone on your home carrier's default roaming.

Use the eSIM if the phone supports one and you mainly need data for maps, mail, and chat. Use a tourist SIM if you need a Thai phone number, or if the phone has a SIM tray and no eSIM. Keep the home SIM able to receive SMS for bank codes when the phone can hold both.

Options compared

Travel eSIM, bought at home. Data in the arrivals hall, no counter, usually no Thai number. The phone has to be unlocked and eSIM-capable.
Tourist SIM from AIS, TrueMove H, or dtac. A Thai number, passport registration at the counter, and you are offline until that is done. Works in a phone without eSIM.
Home-carrier roaming or a daily travel pass. Nothing to buy in Thailand, and the bill is the thing this site is warning you about. See roaming and bill shock.

The longer comparison is eSIM vs a local SIM in Thailand.

Local SIM

The three names you will see on shops and airport counters are AIS, TrueMove H, and dtac.

True and dtac merged in 2023. Telenor announced the completion of the amalgamation on 1 March 2023, and the combined company is True Corporation. Telenor's announcement is the source for the date. Both brand names are still in use. dtac's business FAQ says the dtac and TrueMove H brands continue as two brands under the NBTC's resolution. That FAQ is the source for the brands.

Coverage still differs by region, and it differs again on islands. A brand that is fine in Bangkok can be patchy on a smaller island, and the other way around. Check each operator's coverage map for the places on your route before you rely on one SIM. The maps are on the operators' own sites and they do not match each other.

Tourist SIM

A tourist SIM is a prepaid SIM with a fixed validity. Depending on the package, it usually includes data for a set number of days, and some packages include a limited amount of local calls. The days, the allowance, and what a top-up does after that are printed on the current offer. This page does not list prices or gigabytes. Check the operator's current tourist SIM page:

You need your passport. Registration to a passport is a legal requirement, not a shop preference. The Tourism Authority of Thailand's note on the government site says a SIM is registered with the buyer's name and passport number. That note was updated in January 2023. True and dtac's tourist terms also say the number must be registered with a valid passport under NBTC rules, and they state a limit of no more than three SIMs per person per brand. Those terms, as of October 2026. Buy from an operator counter, an operator shop, or another seller who will do that registration. A loose SIM from a stall that will not register it is a SIM you may not be able to use.

Where people buy them: airport counters on arrival, including Suvarnabhumi (BKK), Don Mueang (DMK), Phuket (HKT), and Chiang Mai (CNX); AIS, True, and dtac shops in town; and convenience stores such as 7-Eleven. The same government note says top-ups are sold at 7-Eleven and at provider stores. Confirm the shop will register the passport before you pay.

Top up at those shops, in the operator's app, or with a code the receipt shows. Checking the balance:

AIS: the tourist plan page says dial *121# for the remaining balance and *121*3# for the remaining package. AIS tourist page.
dtac: *101*9#. TrueMove H: #123#. Both are listed on the Tourism Authority of Thailand note (page updated January 2023). If a code does nothing, check with the operator. These codes are old enough that a menu may have moved.

eSIM

A travel eSIM for Thailand is the option that is ready when the plane lands. Install it on wifi before the flight. It is usually data only, so it does not replace a Thai number and it does not replace the home SIM for bank texts.

Operator eSIMs from AIS, TrueMove H, or dtac are a separate product from the travel-company eSIMs. If you buy one of those, ask whether passport registration can be finished online or still needs a shop visit. Rules on that have been tightened. The travel-company route is covered on the eSIM guide.

Wifi

Hotels, cafes, malls, and the airports offer wifi. Treat it as a shared network: use HTTPS, forget the network when you leave, and do not type a banking password into a captive-portal page. The habits, and the limits of a VPN on that wifi, are on Wifi and VPN.

For how to choose a VPN, use the sister site: Learn how to choose a VPN at VPNPulse.

Practical tips

Download offline maps while you still have a reliable connection. Island ferries and some national parks are the places the signal drops.
LINE is the app shops, hotels, and tour desks commonly use. Install it before you need to message a driver.
Bring a phone that is carrier-unlocked. A locked handset will not take a Thai SIM, and it may refuse a third-party eSIM.
Keep your home number able to receive SMS. Thai and home banks both send one-time codes to the number they have on file, which is often the home number.
Carry a power bank. Navigation and a hotspot drain the phone faster than they do at home, and a dead phone is an offline phone.
Check the coverage map of the SIM you bought before an island or a border trip. Do not assume Bangkok coverage repeats on a smaller island.

VPN

A VPN encrypts the path from your phone to the VPN company's server. On hotel or cafe wifi, the local network then sees that connection rather than the list of sites inside it. A VPN does not prove the wifi name is genuine, and it does not stop a lookalike login page.

Learn how to choose a VPN at VPNPulse. The travel-specific version of the limits is Wifi and VPN.

Check before you go

Data roaming is off on the home line. If you bought an eSIM, it is installed and you know whether the days start on install or on first connection.
The phone is unlocked. Your passport is in your carry-on if you plan to buy a SIM on arrival.
Offline maps are downloaded. LINE is installed if you will use local bookings.
You have looked at a coverage map for any island on the trip.
Once you are online in Thailand, test the connection. Test your connection with NetPulse.