AIS and True both quote roaming add-ons before 7% VAT, and dtac numbers now buy True's packs. For a week in Japan, AIS's 7-day Ready2Fly gives 16 GB for 480 baht with VAT, against 8 GB for the same 480 at True. A travel eSIM is cheaper if you need 5 GB or less.
Search for roaming from Thailand and you get three answers: AIS, TrueMove H and dtac. Two of them are now the same network. Here is what each charges as of 28 October 2026, taken from the carriers' own pages, and the trips where paying them beats buying a travel eSIM.
dtac roaming is now True roaming
In short: dtac numbers now buy True's roaming packs, at True's prices and on True's country list.
True and dtac merged in 2023, and the roaming products have now finished merging too. dtac's roaming pages no longer exist as their own thing: `dtac.co.th/en/ir/gotravel` returns a 301 redirect to True's roaming page, and `dtac.co.th/en/gointer/` redirects to True's GO Travel SIM page.
So the three-way comparison most people think they are making is a two-way one. Hold a dtac number and you are buying True's GO Travel packages, on True's coverage list, at True's prices. True's own page lists both call centres and describes the SIM as compatible with True and dtac alike.
That leaves AIS on one side and True with dtac folded into it on the other. Their headline prices still line up almost baht for baht, 199, 299, 449, 649, but on 28 October 2026 AIS put far more data behind them: 449 baht before VAT buys 16 GB for 7 days at AIS and 8 GB for 10 days at True. Which network you are already on matters less than which pack you pick.
Ready2Fly or SIM2Fly: AIS sells you two different things
In short: Ready2Fly adds data to your own number; SIM2Fly is a second prepaid number on its own SIM.
Both are AIS, both get called roaming, and they are not the same product.
Ready2Fly is an add-on to the AIS number you already carry. Nothing changes in the phone, your number stays live, and the package starts counting when you first connect abroad. AIS's Japan roaming page lists the Asia and Australia packs, which also cover China, South Korea, Malaysia and Singapore: 199 baht for 3 GB or 299 baht for 4 GB over 3 days, 449 baht for 18 GB over 5 days, 16 GB over 7 days or 13 GB over 10 days, 649 baht for 23 GB over 10 days and 849 baht for 28 GB over 15 days. All of those are before 7% VAT.
SIM2Fly is a second prepaid number on a SIM you buy and carry. The Asia and Australia starter is 399 baht, and top-ups run from 119 baht for 1 GB over 2 days to 349 baht for 6 GB over 10 days. It is cheaper per gigabyte at the small sizes. It is also not your number, which matters more than it sounds.
GO Travel, and the VAT hiding in the price
In short: Add-ons on both networks are quoted before 7% VAT; the second-number SIMs include it.
True and dtac sell the same two shapes, listed on True's roaming page. The GO Travel add-on keeps your number: 299 baht for 4 GB over 3 days, 449 baht for 8 GB over 10 days, 649 baht for 16 GB over 10 days, 699 baht for 10 GB over 15 days and 1,299 baht for 15 GB over 30 days, all before VAT. There is no 7-day pack. The GO Travel SIM is the second-number option, 399 baht with VAT for 6 GB over 10 days, currently with a 2 GB bonus on top, plus 2 GB of Thai data for when you get home.
One detail decides several of these comparisons. Both add-ons, AIS Ready2Fly and True GO Travel, are quoted before 7% VAT, while the second-number SIMs, SIM2Fly and the GO Travel SIM, are quoted with VAT included. So a 449 baht add-on is 480 baht at the till on either network, and a 399 baht SIM is 399. Line the headline numbers up without that and the add-ons look cheaper than they are.
Heads-upDo not roam without a package running. AIS bills 0.0049 baht per kilobyte before VAT in all five of these countries, about 5 baht a megabyte or roughly 5,000 baht a gigabyte. True's postpaid day rate is 350 to 499 baht for 1 GB, then 384 Kbps, and where no country and network is specified it bills 450 baht per megabyte. A phone that syncs photos overnight can outspend the airfare.
Where the carriers beat us, and by how much
In short: AIS's 7-day 16 GB pack is about 30 baht a gigabyte, cheaper than our Japan or China plans at volume.
This is the part a shop that sells travel eSIMs is not supposed to put in writing.
The honest split is by trip shape, not by brand.
AIS's 7-day Ready2Fly is 480 baht with VAT for 16 GB, 30 baht a gigabyte, and the 10-day 23 GB pack works out the same. Our Japan plans are 60 baht a gigabyte at the 10 GB tier and China is 54. Fly to Tokyo for a week, genuinely use 10 GB, and Ready2Fly is the cheaper buy. Take it. True's 16 GB GO Travel add-on comes to about 43 baht a gigabyte with VAT.
Two things pull the other way and they decide most real trips. Most carrier Asia packs expire in 3 to 15 days while our plans run 30; True's one 30-day pack is 1,299 baht before VAT for 15 GB. And they are sized for heavy users, so needing 5 GB still means paying for 8 GB at True or 16 GB at AIS.
The honest split is by trip shape, not by brand. In Japan and China, more than 5 GB inside a week goes to AIS. Light use, trips longer than ten days and the cheap-wholesale countries come to us.
The five destinations, and what a week actually costs
In short: For a 5 GB week, our eSIM costs 150 to 335 baht against 480 at either carrier.
Most outbound trips from Bangkok run about a week on 5 GB: maps, LINE, a few hours of video, photos going home. Against that, the cheapest package from each seller that actually fits:
| Destination | Zwitchy 5 GB / 30 days | AIS Ready2Fly 16 GB / 7 days | True and dtac 8 GB / 10 days |
|---|---|---|---|
| China | ฿285 | ฿480 | ฿480 |
| Japan | ฿335 | ฿480 | ฿480 |
| South Korea | ฿185 | ฿480 | ฿480 |
| Malaysia | ฿150 | ฿480 | ฿480 |
| Singapore | ฿185 | ฿480 | ฿480 |
The gap is widest where wholesale is cheapest. South Korea and Singapore come in at 185 baht for 5 GB and 300 baht for 10 GB, and Malaysia is cheaper still at 150 and 250. Those are the three where the carrier bundle is simply the wrong buy for a normal holiday.
Japan is the closest call, at 335 baht for 5 GB and 600 for 10 GB, which is why AIS's 16 GB week pack at 480 baht overtakes us as soon as you need more than 5 GB. China sits in between at 285 and 535. Sizing rather than choosing? The data calculator does that part.
Japan for 7 days: AIS vs True vs dtac
In short: Up to 5 GB, our Japan eSIM is cheapest; from 6 to 16 GB, AIS's 7-day pack wins.
A week in Japan is the version of this question most people ask, so here it is on its own, from AIS's Japan roaming page and True's roaming page as of 28 October 2026. dtac numbers buy from True's list, and only AIS sells a 7-day Asia pack. Carrier prices below include the 7% VAT.
| Package | Data | Days | You pay |
|---|---|---|---|
| AIS Ready2Fly | 16 GB | 7 | ฿480 |
| True / dtac GO Travel | 8 GB | 10 | ฿480 |
| True / dtac GO Travel | 16 GB | 10 | ฿694 |
| AIS SIM2Fly, second number | 6 GB | 10 | ฿399 |
| True GO Travel SIM, second number | 6 + 2 GB | 10 | ฿399 |
| Zwitchy Japan | 5 GB | 30 | ฿335 |
| Zwitchy Japan | 10 GB | 30 | ฿600 |
Under about 5 GB for the week, our 5 GB Japan plan at 335 baht is the cheapest thing here. From 6 GB up to 16 GB, AIS's 7-day Ready2Fly at 480 baht wins, and it keeps your Thai number live for bank OTPs. On True or dtac there is no 7-day pack, so the 8 GB 10-day add-on at the same 480 baht is the match. One Japan detail from AIS's own page: calls on its Japanese partner networks only work with AIS HD Voice (VoLTE) switched on, which is free, so turn it on before you fly. Our Japan guide covers the rest of the trip.
China: everyone bypasses the firewall except a local SIM
In short: A travel eSIM roams too, so Google and WhatsApp usually work without a VPN.
A common piece of advice says you need carrier roaming for China because roaming routes your traffic home before it reaches the internet. The first half is right and the conclusion is wrong.
A travel eSIM roams too. It joins a China Mobile, Unicom or Telecom partner network under a roaming agreement, and that connection also routes internationally, so Google, WhatsApp and Instagram typically work without a VPN. The thing that does not clear the firewall is the local prepaid SIM you buy at a counter in Shanghai, which also wants your passport and, at many stores, a photo.
So on China the choice is not firewall versus no firewall. It is 285 baht against 480, and our China guide covers the rest of the trip.
The OTP your bank sends does not follow a travel SIM
In short: Keep your Thai SIM in with data roaming off and OTP texts still arrive, free.
This is the one that actually ruins trips, and it has nothing to do with data. Thai banks send one-time passwords by SMS to your Thai number. Lose that number for a week and you cannot move money, confirm a card payment, or get back into an app that logs you out.
Ready2Fly and the GO Travel add-on are add-ons to your existing number, so the OTP arrives normally. SIM2Fly and the GO Travel SIM are new numbers and on their own they do not solve it. Neither does a travel eSIM.
The fix is identical in all three cases, and it is free. Leave your Thai SIM in the phone with its data roaming switched off, and run data on the second line. AIS's rate card prices an outgoing SMS at 12 baht and an incoming call at 26 baht a minute, and lists no charge at all for receiving an SMS. Your number stays reachable and costs you nothing.
So what should you buy?
In short: Pick by trip shape: how much data, how many days and how many countries.
Four rules cover nearly every trip out of Suvarnabhumi.
- One country, normal data use, trip longer than ten days: a single-country travel eSIM, every time. The 30-day validity is doing as much work here as the price.
- Three or more countries in one run: our Asia plan covers 26 of them on one eSIM, 670 baht for 10 GB. That is close to the 399 baht SIM2Fly starter per gigabyte, but more than double AIS's week packs at about 30, so buy it for the 30 days and the single eSIM rather than for the price.
- More than 5 GB inside a week in Japan or China: AIS Ready2Fly, 449 baht before VAT for 16 GB over 7 days, or 649 for 23 GB over 10 days. Per gigabyte that beats anything we sell for those two countries, and True's 16 GB add-on too.
- You need your Thai number reachable and you will not carry two lines: an add-on on your own number, from whichever of the two networks you are already on.
Whatever you pick, buy it before you fly. Every option here is cheaper than the pay-per-use rate that switches on automatically the moment your phone finds a foreign network.
Questions travelers ask
Does dtac still have its own roaming packages?
No. Since the merger with True completed, dtac's roaming pages redirect to true.th, and dtac numbers buy True's GO Travel packages on True's coverage list. Checked again 28 October 2026: dtac.co.th/en/ir/gotravel returns a 301 to True's roaming page. Your dtac SIM keeps working; the roaming product behind it is True's.
Is dtac still a separate brand in 2026?
As a brand, yes: dtac numbers and SIMs carry on, and True's roaming page still has a dtac tab and the dtac call centre, 1678. Behind it is one company, True Corporation, since the 2023 merger, so dtac's roaming packs, country list and prices are True's.
Which is cheapest for 7 days in Japan: AIS, True or dtac?
AIS. Its 7-day Ready2Fly pack is 449 baht before VAT, 480 with it, for 16 GB. True has no 7-day pack; its closest, 8 GB over 10 days, costs the same 480 with VAT for half the data, and dtac numbers buy True's packs. If you need 5 GB or less, a 5 GB Japan eSIM at 335 baht beats both.
Do AIS and True roaming prices include VAT?
Not the add-ons. AIS Ready2Fly and True GO Travel are quoted before 7% VAT, so 449 baht becomes 480 at the till. The second-number SIMs, AIS SIM2Fly and the True GO Travel SIM, are quoted with VAT included, and pay-per-use roaming on both networks is quoted before VAT.
Is SIM2Fly or a travel eSIM cheaper?
For a normal one-week trip, the eSIM. SIM2Fly's Asia and Australia starter is 399 baht, against 150 to 335 baht for a 5 GB eSIM to the five most popular destinations, and the eSIM runs 30 days instead of 10. SIM2Fly wins if you want a physical SIM you can reuse and top up across several trips.
Will my Thai bank OTP still arrive if I use a travel eSIM?
Yes, as long as you leave your Thai SIM in the phone and keep the line enabled. Turn data roaming off for that line and run data on the eSIM instead. Incoming SMS is not charged on AIS's published rate card, so the number costs you nothing while you are away.
Do I need a VPN in China with a travel eSIM?
Usually not. A travel eSIM roams onto a Chinese partner network and the connection routes internationally, so Google, WhatsApp and Instagram typically work without one. It is the local prepaid SIM bought at a counter in China that sits behind the firewall.
What happens when I use up a carrier roaming package?
You are throttled, not cut off. Both AIS SIM2Fly and True's GO Travel SIM drop to 128 Kbps once the allowance is gone, and True's postpaid day pass drops to 384 Kbps after its first gigabyte. The exception is AIS's 2,799 baht SIM2Fly Global card, which stops instead of slowing.
How much does roaming cost with no package at all?
Enough to notice for years. AIS charges 0.0049 baht per kilobyte before VAT, about 5 baht a megabyte, in all five of these countries. True charges 350 to 499 baht a day for a gigabyte, or 450 baht per megabyte where the country and network are not specified.
Which is better for a multi-country Asia trip?
It depends how much data you need. Our Asia plan covers 26 countries at 670 baht for 10 GB, about 67 baht a gigabyte. That is close to the 399 baht SIM2Fly starter but more than double AIS's Ready2Fly week packs at about 30 with VAT, which cover 31 Asia and Australia countries. Buy ours for the 30 days and the one eSIM across every border; buy AIS's if you will use 10 GB or more inside a week or ten days.
Sources
Written by the Zwitchy team. Updated Oct 28, 2026.
- True's roaming page · true.th
- AIS's Japan roaming page · ais.th
- SIM2Fly · ais.th
- GO Travel SIM · true.th
Get a travel eSIM for 200+ destinations in under a minute.
Get your Asia eSIM →
