Thailand’s three major carriers — AIS, DTAC (now merged into True Move H), and TrueMove H — give good urban coverage and reasonable island coverage for the major resort destinations. The eSIM market here is mature and competitive: multiple providers offer Thailand plans, prices are low, and activation is smooth. The honest question for most visitors is whether to buy an eSIM before arrival or pick up a local physical SIM at the airport, and the answer has shifted decisively toward eSIM in the last two years for any device that supports it.

Yesim covers Thailand on the AIS or TrueMove network depending on the package tier. AIS is the largest carrier by subscriber count and has the strongest island coverage — Koh Samui, Koh Tao, Koh Lanta, and Koh Phi Phi all have functional AIS signal in accommodation zones and beach fronts. Yesim’s Thailand packages run approximately $6-$10 USD for 7 days/2GB and $15-$22 for 30 days/10GB. Tethering is supported, which matters for travellers working remotely from Thai beach cafés — a common use case. The activation-before-travel flow works cleanly: install the profile on the plane, turn the eSIM on when you land at Suvarnabhumi.

Airalo is the most competitive on price for Thailand. Its local AIS-network package typically runs $4-$6 for 7 days/1GB and $10-$14 for 15 days/3GB, making it the strongest choice for a shorter trip where high-volume streaming is not the priority. Airalo’s regional Asia eSIM is worth comparing if Thailand is part of a multi-country circuit (Japan-Thailand-Vietnam): a single regional plan avoids the need to install separate country SIMs for each leg.

Saily covers Thailand competently and is worth considering if privacy matters to you — their infrastructure avoids the data-brokering model that some low-cost providers rely on to subsidise cheap plans. Data caps at the higher tiers are slightly more limited than Airalo, but for typical browsing, Google Maps, and messaging, the practical difference is small.

The local SIM comparison: DTAC and AIS tourist SIMs sell at Suvarnabhumi Airport arrivals and at 7-Eleven stores countrywide for approximately THB 299 (£7) for 30 days/8-15GB. This is cheaper in raw data-per-baht terms than any eSIM option. The argument against it: the airport SIM counters run queues after major international arrivals, you get a physical card that can fall out of your pocket, and returning to a dual-SIM setup (home SIM + Thai SIM) means your domestic number goes offline. For a traveller on a single trip with two weeks or more in Thailand, a local physical SIM is a reasonable choice. For travellers doing Thailand as part of a longer Asia circuit, or those with newer phones managing multiple profiles, eSIM removes friction that compounds over a long trip.

Island coverage is worth specifying. Koh Tao is the island where coverage is most variable: the interior is hilly and some bungalow clusters away from the main beach have limited signal regardless of carrier. Download offline maps before the ferry. Koh Lanta’s southern tip has patchy coverage. The Phi Phi Islands, Koh Samui, and Krabi Town all have strong coverage from all major providers. On the mainland, Chiang Mai, Pai, and the Golden Triangle all have functional data coverage; the Mae Hong Son loop through mountain curves has intermittent signal in the valleys, which is part of the attraction.

One thing to verify before purchase: some eSIM plans in Thailand are data-only with no voice capability. If you need to call local numbers (tuk-tuks, guest houses, activity operators), confirm the plan includes voice or a VoIP option. Most travellers manage entirely on WhatsApp and messaging apps, but it is worth knowing before you need to make an urgent call.