Choose your Thailand eSIM based on your route, not just the price. Thailand's mobile market runs on two networks, AIS and True, and while both work well in Bangkok, Chiang Mai, and Phuket, only one of them holds a signal reliably once you're island-hopping or heading into the mountains. This guide covers how eSIMs work in Thailand, which network to pick for your itinerary, and how much data you actually need.
Why Network Choice Matters More in Thailand Than Elsewhere
Thailand's mobile market consolidated in 2023, when True absorbed DTAC, and the two networks finished integrating their towers in 2025. AIS and True now both deliver strong 4G and 5G in the cities and main tourist areas. The difference shows up once you leave them. AIS holds signal better on remote islands like Koh Tao, Koh Lipe, and Koh Kood, on mountain routes like the Pai loop and Doi Inthanon, and reconnects faster after a ferry crossing. True performs just as well in busy tourist zones but fades faster on quieter beaches and interior roads. Ferry crossings between islands lose signal on every network, since that's open water, not a coverage gap specific to any provider.
Do You Need an eSIM for Thailand?
Check your Belgian plan's Thailand coverage before you fly, not after you land. Thailand is far outside the EU roaming zone, so your provider will usually bill it at standard non-EU rates unless you've added a specific pass. For most trips, especially anything longer than a few days or involving islands and rural travel, an eSIM works out cheaper and gives you a clearer idea of what you're paying upfront.
How Much Data Do Light Users Actually Need?
| Activity | Typical Data Use |
| Google Maps Navigation (1 hour) | 5-10 MB |
| WhatsApp texts or LINE messages + a few photos (per day) | 10-20 MB |
| Digital Boarding Pass or Hotel Confirmation | Under 1MB |
| Grab hailing app (per booking) | 5-10 MB |
| Light Browsing or Email (30 minutes) | 15-25 MB |
Add it up and a light-use day in Thailand, maps in Bangkok, LINE with your hotel, a Grab booking, some browsing, usually lands between 60 and 120 MB. A week of light use rarely clears 1 GB. A small eSIM bundle covers this comfortably, and it's considerably cheaper than non-EU roaming rates.
If your travel days look like this, a small eSIM bundle is often all you need. Instead of paying non-EU roaming rates by the day, a 1GB Firsty eSIM covers maps, messages, boarding passes and the occasional ride booking with room to spare.
Check our plans and set it up before you land, so you're connected from the moment you touch down.
eSIM vs Physical SIM in Thailand
An eSIM suits most trips: no SIM shop counter, no swapping your existing card, and your Belgian number stays active for calls and texts while the eSIM handles data. A physical Thai tourist SIM can be cheaper for a longer stay and is easy to buy at the airport or in convenience stores, but it means carrying a second card and losing your usual number for the trip. Check device compatibility first: most iPhones from the XR onward and recent Samsung Galaxy or Google Pixel models support eSIM.
What to Check Before You Book a Thailand eSIM
Confirm which network the eSIM actually runs on using the table above, since a generic "unlimited Thailand" plan can still leave you without signal on a quiet island. Match your data allowance to your route with the usage table above rather than defaulting to a large bundle. Check the price is stated clearly upfront, and confirm whether the plan includes calls and texts or is data only, since most Thailand travel plans are data-only.
Where Firsty Fits In
Check whether your Firsty plan already covers Thailand before you fly, since it sits far outside the EU roaming zone and isn't included by default the way EU countries are. If it isn't, a Thailand eSIM works the same way as any other Firsty plan: no zone chart to check, no roaming toggle to flip, and no surprise bill once you're home. Check current plans, pricing, and network coverage for Thailand.
FAQ
Do I need an eSIM for Thailand? Not strictly, but it's usually the cheaper option. Without one, you're relying on your Belgian roaming rate, which is billed at non-EU rates since Thailand is far outside the EU roaming zone.
What is the best eSIM for Thailand? It depends on your route. For Bangkok, Chiang Mai, and Phuket, most eSIMs work well. For remote islands or mountain routes, choose one that specifically runs on AIS.
Does my Belgian phone plan cover Thailand? Not automatically. Thailand is outside the EU roaming zone, so check your operator's app for a Thailand-specific pass before you travel.
Will my eSIM work on ferries between islands? Expect gaps on open water regardless of network or provider. Signal typically returns as you approach the next island.
How much data do I need for a week in Thailand? Light users typically stay under 1 GB for a full week. Heavier use, navigation-heavy travel or hotspot sharing, needs more.
