Buy the SIM Card at the Airport, Then Immediately Do This
The airport SIM is more expensive than the city SIM by about 40 per cent, and the difference buys you one thing: not missing a flight home because a taxi driver had the wrong number.
The mobile data question in Thailand is unusually easy to get right and unusually easy to get wrong, because the thing that catches people is not the price, it is the date.
Last verified 25 September 2026.
Buy it, yes, but know what you are paying for
Airport SIMs cost roughly 40 to 60 per cent more than the identical SIM in the city. The airport counters are operated by the carriers and the price includes the convenience of walking straight out of arrivals with a working phone. A 15-day tourist package with a generous data allowance is commonly 900 to 1,200 baht at Suvarnabhumi and 500 to 700 baht for the same thing in Chiang Mai or on the street.
That gap is real money across a two-week trip. It is also, for most people, worth paying once, because the alternative involves standing in a shop queue on your second morning holding a passport you would rather not hand over to a stranger.
Read the date on the package, not the price
This is the trap and it catches a large share of visitors. Thai tourist SIMs are valid for a limited number of days from activation, and the countdown starts the moment the card is switched on, not when you arrive and not when you use it.
A 15-day package might expire on day 14 at 11pm with two days of trip left, and a 7-day package on a 10-day trip will die on day 7 with no warning beyond a sudden loss of signal.
Before you leave the counter, photograph the printed expiry date and check it against your departure date. This takes fifteen seconds and it is the only mobile advice in Thailand that reliably matters. If the counter will not tell you, look at the card or the receipt. If neither shows it, buy a second card later in the trip and use both, which is a perfectly normal thing locals do.
The roaming trap, which is separate and worse
Buying a SIM does not stop your home network roaming if your phone still has your home SIM in it or your phone is set to prefer a network you own. Data can be charged at a genuinely alarming rate.
Check before you leave the airport. If you are carrying a travel eSIM, confirm it is what is actually routing your data, not a physical Thai SIM sitting in the tray. If you have both, turn the roaming one off. On iPhone this is in Cellular settings per line; on Android it is under the SIM's own settings, not the main mobile data menu, which is where people fail.
The symptom to watch for is a phone that is on WiFi all evening and suddenly cannot find a network on the way to the airport. That is a roaming bill forming.
What coverage is actually like
All three major operators cover Bangkok, the airport, the major tourist belts, and the islands, and the differences between them are not worth optimising for unless you are going somewhere specific.
Where coverage genuinely gets thin: deep inside national parks and on some of the smaller islands on the Andaman side, particularly Koh Lanta's interior and the more remote Gulf islands. The rail lines between Bangkok and the south are covered. The 1 and 2 motorways are covered. The 4 through the Isan is patchy in places and the 12 in the north has been improved substantially but is not uniformly good.
Do not pick an operator on a coverage map that is obviously wrong. AIS, True, and dtac are all fine. The counter staff will recommend one and the recommendation is not going to save your trip.
Hotspot versus eSIM
If you travel with a laptop, decide this before you fly because the maths is different.
A Thai SIM in a hotspot is cheap and works everywhere a phone does. A 15-day package with enough data for a working trip is a few hundred baht.
A travel eSIM is cheaper and does not tie you to a carrier, but it needs a compatible phone and the eSIM providers are more variable in quality than the local carriers.
If you are on a phone that supports a physical SIM and a hotspot, the Thai SIM is the boring reliable choice. I have had a Thai SIM in a hotspot in a place with no local signal and the hotspot kept working, which a roaming eSIM from another country would not have.
One practical thing to ask for
Ask the counter for the number written on a card, not just told to you, and put it in your phone before you leave. The reason is not that you will lose the SIM, it is that you will need to top up, and topping up a Thai SIM generally requires either a physical top-up card or a specific app, and neither is something you want to figure out in a queue.
Also ask whether the package is throttled after a data limit rather than cut off. A throttled connection still lets maps and messages work, which can be the difference between getting somewhere and not.
