AIS vs True vs dtac roaming: what it really costs
AIS and True sell Asia roaming at roughly 43 to 66 baht per gigabyte, and dtac's roaming is now True's. A travel eSIM runs 25 to 60 baht per gigabyte. For a normal one-week trip the eSIM is cheaper to all five of Thailand's top destinations. For a 15 GB trip to Japan it is not.
Contents
- dtac roaming is now True roaming
- Ready2Fly or SIM2Fly: AIS sells you two different things
- GO Travel, and the VAT hiding in the price
- Where the carriers beat us, and by how much
- The five destinations, and what a week actually costs
- China: everyone bypasses the firewall except a local SIM
- The OTP your bank sends does not follow a travel SIM
- So what should you buy?
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 17 September 2026, taken from the carriers' own pages, and the trips where paying them beats buying a travel eSIM.
dtac roaming is now True roaming
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. They price within a few baht of each other, which is why the brand is the least interesting part of this decision.
Ready2Fly or SIM2Fly: AIS sells you two different things
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. Asia and Australia pricing runs 199 baht for 3 GB over 3 days, 449 baht for 8 GB over 10 days, and 649 baht for 15 GB over 10 days, VAT included.
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
True and dtac sell the same two shapes. 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. The GO Travel SIM is the second-number option, 399 baht for 6 GB over 10 days, with 2 GB of Thai data thrown in for when you get home.
One detail decides several of these comparisons. True quotes its add-on prices excluding VAT; AIS quotes Ready2Fly including it. True's 449 baht package is 480 baht at the till, against 449 baht flat for the AIS one. Line the two headline numbers up and you get the answer backwards.
Do 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
This is the part a shop that sells travel eSIMs is not supposed to put in writing.
AIS Ready2Fly at 649 baht for 15 GB is 43 baht a gigabyte. Our Japan plans are 60 baht a gigabyte at the 10 GB tier and China is 54. Fly to Tokyo for ten days, genuinely use 15 GB, and Ready2Fly is the cheaper buy. Take it. True's 16 GB GO Travel add-on lands at the same 43 baht a gigabyte.
Two things pull the other way and they decide most real trips. The carrier Asia bundles expire in 3 to 15 days while our plans run 30. And they are sized for heavy users, so needing 5 GB still means paying for 8 or 15.
The honest split is by trip shape, not by brand. Heavy use inside ten days goes to the carriers. Everything else comes to us.
The five destinations, and what a week actually costs
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 8 GB / 10 days | True and dtac 8 GB / 10 days |
|---|---|---|---|
| China | ฿285 | ฿449 | ฿480 |
| Japan | ฿335 | ฿449 | ฿480 |
| South Korea | ฿185 | ฿449 | ฿480 |
| Malaysia | ฿150 | ฿449 | ฿480 |
| Singapore | ฿185 | ฿449 | ฿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 the 15 GB Ready2Fly package overtakes us at volume. China sits in between at 285 and 535. Sizing rather than choosing? The data calculator does that part.
China: everyone bypasses the firewall except a local SIM
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 449, and our China guide covers the rest of the trip.
The OTP your bank sends does not follow a travel SIM
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?
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 matches the 399 baht carrier starter per gigabyte, but sits well above their 15 GB bundles at 43, so buy it for the 30 days and the single eSIM rather than for the price.
- Fifteen gigabytes or more inside ten days: AIS Ready2Fly at 649 baht, or True's 16 GB add-on. They are cheaper per gigabyte than anything we sell for Japan or China.
- 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.
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 17 September 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 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 Global package, 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, which matches the 399 baht carrier starter but sits well above the 15 GB carrier bundles at roughly 43. Buy ours for the 30 days and the one eSIM across every border; buy theirs if you will genuinely use 15 GB inside ten days.
