eSIM Coverage on Thai Islands (Koh Samui, Koh Phangan)

Which operator reaches the islands furthest

AIS and TrueMove H both cover the main Thai islands well, and they differ on the smaller islands, the boat legs, and the interior roads. AIS holds the more consistent signal on Koh Lanta, Koh Yao, Koh Tao, and Koh Phangan's quieter stretches, dropping less often than TrueMove during ferry crossings and on interior roads. TrueMove H performs strongly in Phuket and Phi Phi's main tourist areas but grows uneven once away from those zones, fast in one bay and weak in the next, and a traveler covering a full island-hopping route should buy a plan attached to AIS, detailed further in Saily island network position.

Operator reach across the islands is shown in the table below.

Koh Samui

Koh Samui is the best covered island in Thailand, with dense coverage across Chaweng, Lamai, Bophut, and the ring road. AIS runs slightly ahead of TrueMove H across most of the island, though both networks handle everyday browsing, messaging, and video calls without issue in the main tourist strip.

Coverage by area on Koh Samui is shown in the table below.

Koh Phangan

Koh Phangan is well covered in Thong Sala, Haad Rin, and the main west coast beaches, and thin across the interior and the northern bays. Coverage holds reliably in the island's populated south, where most accommodation and the ferry pier sit, then weakens noticeably moving north and inland.

Coverage by area on Koh Phangan is shown in the table below.

The Full Moon Party congestion effect

Tens of thousands of people gathering on one beach overload the local cells, and a wholesale travel eSIM is slowed before the operator's own direct subscribers. Expect noticeably slower data at Haad Rin on the night itself, even though the underlying AIS or TrueMove H signal remains physically present, the sheer device density on one stretch of sand saturates the local towers. Arranging a physical meeting point with a travel group in advance matters more than usual, since messaging apps may lag under the congestion. Downloading a map of Haad Rin and completing any needed top up earlier in the day, before the crowd builds, avoids relying on a connection that slows sharply after dark, a pattern comparable to the Full Moon crowd effect seen during Pattaya's own peak tourist congestion.

Koh Tao and the northern Gulf

Koh Tao holds solid coverage in Sairee and Mae Haad, its two main population centers. Both AIS and TrueMove H maintain reliable 4G in these areas, supporting normal browsing, messaging, and photo uploads without difficulty. Dive sites, viewpoint trails, and the island's eastern bays sit outside this reliable zone, particularly the stretch of water between Koh Tao and Koh Nang Yuan, where signal frequently drops to nothing.

The Andaman islands

The Andaman islands are covered in the main village areas and drop away quickly on the boat routes and the national park islands. Phi Phi and Koh Lanta hold the strongest signal of this group, since both carry enough tourist infrastructure to support dense tower coverage in their main villages. The Similan and Surin islands sit apart entirely, protected national parks with essentially no cellular infrastructure at all, a gap detailed further alongside Krabi and Lanta detail.

Coverage by island in the Andaman group is shown in the table below.

Coverage on the ferry legs

Coverage extends a short distance from shore and then stops, so most Thai ferry crossings include a stretch with no signal at all. Crossing time and the expected point of signal loss vary meaningfully by route, generally lasting longest on the routes that pass through open water rather than staying close to a chain of islands, with the longest gap running on the Krabi to Phi Phi and Phuket to Phi Phi legs, detailed further in boat legs from Phuket.

Ferry route signal position is shown in the table below.

What to arrange before boarding

Preparing before boarding matters more on Thai ferry routes than it does on the mainland, since a signal gap mid-crossing is close to guaranteed.

Follow the five steps below before boarding a Thai island ferry.

• Save the accommodation address offline. This is the one travelers regret skipping most, since arriving at a pier with no signal and no saved address leaves no way to confirm pickup or directions.
• Arrange the pier pickup in advance. Confirm with accommodation or a taxi contact before departure, since coordinating this mid-crossing is unreliable at best.
• Download the onward route. Save offline maps for the route from the arrival pier to the final destination.
• Note the return ferry time. Screenshot or write down the schedule, since checking it later may mean no signal is available.
• Top up or confirm data balance beforehand. Handle any plan top up before boarding rather than assuming it can be done mid-crossing.

Speed on the islands

Speed across the main island towns typically runs 35 to 55 Mbps on 4G, with AIS generally holding the upper end of this range and TrueMove H sitting slightly behind. High season brings a seasonal congestion effect, since more travelers sharing the same towers in Chaweng, Haad Rin, or Phi Phi's main village slows real-world speeds below what an empty-network test would show. Off-season months typically see speeds closer to the top of the observed range, since fewer devices compete for the same island 5G availability.

How much data does an island trip use?

An island trip uses roughly 1.5 GB to 3 GB per day, driven by photo and video uploads and by boat and accommodation bookings made on the move. A light user relying mainly on messaging and occasional maps typically stays around 500 MB to 1 GB per day. A moderate user mixing maps, social browsing, and some photo uploads runs closer to 1.5 GB to 2 GB per day. A heavy user posting frequent photos and video, or streaming, pushes usage to 2.5 GB to 3.5 GB per day, the heaviest consumer in this range being video uploaded from the beach each afternoon. A booking-heavy user making frequent ferry, hotel, and tour reservations on the move adds another 1 GB to 2 GB per day on top of general browsing. A 10 day island route at moderate to heavy use points toward a 20 GB to 30 GB plan, sized in full at island trip plan sizing. Saily also offers an optional phone number add-on beyond data alone, pairing the standard eSIM with a real, US-based wireless number for voice calls and SMS, useful for a traveler coordinating ferry pickups or accommodation by phone rather than messaging apps alone.

Island coverage questions

Coverage gaps, ferry signal loss, and network choice raise the most common questions travelers ask before an island-hopping trip in Thailand. Answers below cover which islands are reliably covered, how ferry crossings behave, and whether a separate plan is needed for the islands. Each answer below mirrors its own question directly before expanding.

Does my eSIM work on Koh Samui?

Yes, an eSIM works on Koh Samui. Chaweng, Lamai, Bophut, Maenam, and the island's ring road all carry strong, reliable 4G coverage on both AIS and TrueMove H. The interior hill roads, the approaches to Na Muang and Hin Lad Falls, and the quieter south coast near Thong Krut are the areas where signal thins.

Is there signal on the ferry between islands?

Yes, most Thai ferry routes hold signal near both departure and arrival shores, then lose it for a stretch mid-crossing. The gap runs roughly 20 to 45 minutes on longer open-water routes like Krabi to Phi Phi or Phangan to Tao, and closer to a few minutes or not at all on short hops like the Lanta crossings.

Which operator is best for the Thai islands?

AIS is best for the Thai islands. AIS holds the more consistent signal across Koh Lanta, Koh Yao, Koh Tao, and Koh Phangan's quieter areas, dropping less often than TrueMove H during ferry crossings and on interior roads. Multiple independent network comparisons in 2026 rank AIS ahead specifically for islands and remote travel, while TrueMove H remains competitive in Phuket and Phi Phi's main tourist zones.

Will my data work during the Full Moon Party?

Yes, slowly, since tens of thousands of people crowding onto Haad Rin beach overload the local cells, so a travel eSIM slows well before the network itself goes down. Arranging a physical meeting point, downloading a map of the area, and completing any data top up earlier in the day, before the crowd builds, avoids depending on a connection that degrades sharply after dark.

Do the Similan or Surin islands have coverage?

No, both island groups have protected national park status, so cellular infrastructure is minimal. Conservation rules restrict permanent development, including cell towers, causing mainland signals to stop near park boundaries. Boats near the islands may occasionally receive weak distant signals, but coverage remains unreliable. Day-trip boats visiting the Similan or Surin islands usually depart from mainland piers with normal connectivity, then lose signal after entering park waters. Travelers should treat the full day as offline and download maps, schedules, and accommodation details beforehand. The lack of infrastructure affects AIS, TrueMove H, and travel eSIMs equally across both island groups.

Is there 5G on the islands?

5G on the Thai islands remains limited compared to the mainland. Bangkok and a handful of major mainland cities carry the strongest 5G buildout, while island coverage runs predominantly on 4G, which handles typical travel use, messaging, maps, and browsing, without issue. Some main island towns on Samui and Phuket carry pockets of 5G, though it is not consistent across the islands the way 4G is.

Do I need a different plan for the islands?

No, a separate plan is not needed for the islands. One national Thailand eSIM plan, attached to AIS or TrueMove H, covers the mainland and the islands together, since both operators extend their networks to the populated island areas covered on this page. The coverage gaps that exist on ferry crossings and remote park islands apply regardless of which specific plan is purchased.

What should I download before a boat trip?

Downloading the right information before a boat trip prevents relying on a connection that isn't there mid-crossing. Most Thai ferry routes lose signal for a stretch of open water, so anything not already saved offline becomes unreachable at the exact moment it might be needed. Preparing these items on shore, before boarding, removes that risk entirely.

The five items to download before a boat trip are listed below.

• Accommodation address: Confirms the exact destination once ashore, without needing signal to look it up.
• Onward route or offline map: Covers navigation from the arrival pier to the final destination.
• Return ferry schedule: Avoids needing to check departure times while offline.
• Pier pickup confirmation: Screenshots or saved messages confirming who is meeting the ferry, if arranged.
• Any booking confirmations: Hotel, tour, or onward transport confirmations saved as screenshots rather than relying on email access mid-crossing.