Connectivity on landing: SIM, eSIM and keeping your home number.

The networks, in general terms

Thailand's mobile market is concentrated in a small number of operators. AIS is the largest by subscriber base and generally regarded as having the broadest coverage, particularly in rural provinces and on the smaller islands. True is the other major private operator, following the consolidation of the True and dtac businesses, and remains strong in Bangkok and the major cities; the dtac brand has continued to appear on tourist products. NT, the state operator formed from the merger of the old TOT and CAT businesses, is the smaller third player and less commonly chosen by visitors.

For a visitor in Bangkok, Phuket, Chiang Mai or any of the mainstream destinations, all of them are perfectly adequate; speeds on 5G in central Bangkok are genuinely fast and 4G coverage is close to universal. The distinction only starts to matter in remote provinces, on the smaller islands and out at sea, where AIS's rural footprint is the usual recommendation. If your itinerary is entirely urban, choose on price and convenience rather than on network.

eSIM before departure, or a counter on arrival

These are the two real options and the honest answer is that eSIM has become the better default for most travellers, with one important qualification about the phone. An eSIM is a digital profile you buy online and install before you fly, so that you land with data already working, before you have cleared immigration, which is precisely when you want a map, a car and a message to whoever is meeting you. A physical SIM from an airport counter is bought after you land, involves a queue and a passport, and takes ten to twenty minutes you may not want to spend.

The qualification: your handset must be eSIM capable and must not be network locked. Most flagship phones sold in the last several years support eSIM, but not all models in all markets do, and a phone bought on a carrier contract may be locked. Check both before you buy a profile, because a locked phone and a purchased eSIM is money spent on nothing. Check also that your phone supports dual SIM operation with one eSIM and one physical SIM active simultaneously, which is the configuration that solves the home number problem below.

Pricing on both moves constantly and varies by package, so treat any figure you read as indicative. In broad terms, short tourist data packages are inexpensive by international standards, longer packages with generous or unlimited data are excellent value, and airport counters price at a premium to what the same operator charges in a city shop. Do not agonise over the difference; the amounts involved are small relative to the inconvenience of arriving without data.

Buying at the airport, practically

The operator counters sit in the arrivals area at Suvarnabhumi, Don Mueang, Phuket and Chiang Mai, after customs, and they are staffed by people who do this all day in English. You will need your passport, because SIM registration against identity documents is a legal requirement in Thailand and applies to visitors as well as residents. The counter staff will register, fit and configure the SIM for you and will usually test it before you walk away, which is worth waiting for.

• Bring the passport, not a photocopy. Registration is mandatory and the counter cannot proceed without it.
• Ask them to keep and hand back your home SIM in the little tray. This is the most commonly lost item of any arrival.
• Say how long you are staying and how you use data, and let them recommend the package. Do not buy the largest one by default.
• Confirm the SIM works before leaving the counter: load a map, send a message.
• Note the Thai number down somewhere other than the phone itself.
• Top up later through the operator's app or at any convenience store, where the process takes a minute.

Keeping your home number alive, which is the part that matters

For the clients we serve this is the single most important connectivity decision, and it has nothing to do with Thai data. Your bank sends one time passcodes by SMS to your home mobile number. So does your brokerage, your credit card issuer, your government identity service and, quite possibly, your office. If that number stops receiving messages the moment you land, you cannot authorise a payment, release a card block or log into anything that matters, and you will discover this at the worst possible moment.

Three practical additions. Enable wifi calling on your home number before you travel, if your operator supports it, because it lets calls and sometimes messages reach you over any internet connection without roaming charges. Where your bank offers an authenticator application or an in app approval instead of SMS codes, move to it before you leave; it is more secure and it removes the dependency on a network entirely. And tell your bank you are travelling, through the app rather than by telephone, so that a Thai transaction does not trigger a freeze on the card you were relying on.

Islands, boats and the places coverage thins

Mainland Thailand and the developed islands are well covered. Bangkok, Chiang Mai, Phuket, Samui, Pattaya and Hua Hin all have solid 4G with widespread 5G in the centres. The picture changes as you go smaller and further out.

Two mitigations that cost nothing. Download offline maps for every island and province on the itinerary before you leave the mainland. And, where a boat crossing is involved, send the arrival details to whoever is meeting you before you board rather than assuming you can message from the water. Resort wifi on the islands is generally good in the public areas and variable in the villas, so a hotspot from a phone with a decent Thai package is often the more reliable connection for anyone who has to work.

For longer stays and households

Anyone staying months rather than weeks should move off tourist packages onto a standard prepaid or postpaid plan, which is substantially better value and available at any operator shop with a passport and, for postpaid, usually additional documentation. Home fibre in Bangkok condominiums is fast, cheap and installed quickly, and for a family taking a serviced apartment for a season it is worth arranging in the first week rather than living on mobile data. Households with staff should note that Thai numbers are the practical basis for the group chats through which everything gets coordinated, so a local number for the principal, not only for the household manager, saves a surprising amount of friction.

Network branding, package pricing and coverage in Thailand change regularly, and SIM registration requirements are set by the regulator. Confirm current packages and coverage with the operator directly, confirm your handset is unlocked and eSIM capable with your own carrier before purchase, and confirm your bank's alternatives to SMS authentication before you travel.

This briefing is general information, not legal, tax or investment advice. Thai rules change frequently and individual cases differ. Verify current requirements with the relevant authorities, including the Immigration Bureau, the Board of Investment, the Land Department, the Department of Business Development and the Revenue Department, and take advice on your own facts before acting.