Does WiFi Calling work abroad? Calling home to Thailand and what it costs

Thai travellers keep running into the same problem: they want to take calls from the bank, family or work on their Thai number, but they do not want to switch on roaming, which charges for incoming calls by the minute. WiFi Calling solves much of this. This article is about using it in practice abroad. For screen-by-screen setup, see our separate setup guide.

WiFi Calling setup guide before you travel

Does WiFi Calling work abroad?

Yes, as long as WiFi Calling was switched on for your Thai number while you were still in Thailand and your phone has an internet connection. Abroad you can then make and receive calls on your usual number as if you were at home, without using the local mobile network.

Under the hood, the phone builds an encrypted IPsec tunnel over the internet to a gateway called the ePDG on your Thai carrier's network, then registers with the same IMS core that VoLTE uses. This is the 3GPP standard the GSMA profiles as VoWiFi (GSMA PRD IR.51). To the carrier's system you look like a subscriber calling from inside Thailand who happens to be on Wi-Fi instead of a cell tower, which is why the call is billed on your domestic package.

Four conditions have to hold: the SIM or eSIM must be active (not suspended), the phone must support WiFi Calling with that carrier and run current software, the feature must have been switched on in Thailand, and the Wi-Fi you use must not block VoWiFi traffic. If any one is missing, the call either fails or goes out over roaming instead.

Do AIS, True and dtac differ when you use WiFi Calling abroad?

All three are listed on Apple's carrier-features page as supporting Wi-Fi Calling on iPhone, and all now use the native feature (no app). The differences are in how you switch it on for Android and in each carrier's advice. NT Mobile also offers the service and states that it works both in Thailand and abroad.

Since True and dtac merged, dtac's old WiFi Calling page redirects to true.th, and the current setup guide covers both brands. If you are on dtac, follow True's page. The call-centre numbers above work from inside Thailand; from abroad, use the chat in your carrier's app, since overseas contact numbers can change.

How to turn on WiFi Calling on any carrier and phone

How much does it cost to call Thailand with WiFi Calling?

A call to a Thai number is taken from the minutes in your package, and once those run out it is charged at your plan's normal domestic rate. True states that usage is billed on your current package with no special charge; NT states that outgoing calls are billed at package rates and incoming calls are free. The per-minute price therefore depends on your own plan, and there is no single figure that applies to everyone.

The other cost is data. WiFi Calling uses little: the figure commonly quoted is roughly 0.5–1 MB per minute of voice (an estimate, not an official constant). On hotel Wi-Fi that costs nothing extra; on a travel eSIM it comes out of that eSIM's allowance.

Can you receive calls and SMS from Thailand over WiFi Calling abroad?

Yes for calls. Someone in Thailand dials your normal number and pays a normal domestic call; they cannot tell you are abroad. You pay no roaming charge for answering, as long as the phone is registered on WiFi Calling. If you drop off Wi-Fi while your Thai line still has roaming active, the call can come in over a foreign network instead and be billed as a roaming call. That is why the carriers tell you to keep Airplane Mode on.

SMS can travel over IP inside the IMS system (SMS over IP), and many users report bank OTPs arriving normally on WiFi Calling. Thai carriers do not clearly guarantee this on their official pages, though, and some senders only deliver over the mobile network. Before you travel, request one OTP at home in Airplane Mode with Wi-Fi on. If it does not arrive, switch the bank's verification to in-app approval before you fly.

Getting SMS and OTP codes while abroad

Which countries block WiFi Calling or make it unreliable?

Thai carriers publish no official list of countries where WiFi Calling is blocked, and no body such as the GSMA or 3GPP keeps one. Lists on blogs usually mix up bans on internet-calling apps (WhatsApp, FaceTime) with carrier WiFi Calling, which is a different thing. What is better documented:

• United Arab Emirates: the regulator blocks most app-based calling. Local carriers' own Wi-Fi Calling works, but travellers using a foreign SIM's WiFi Calling over hotel Wi-Fi report mixed results.
• China: foreign apps such as WhatsApp and FaceTime are restricted by the Great Firewall. Whether a Thai SIM's WiFi Calling gets through in China has not been confirmed either way by an official source, so have a backup plan.
• A 2024 study (arXiv) found that some operators worldwide geoblock their own customers from using VoWiFi from abroad, based on IP location, mostly in Europe and India. The study does not mention Thai carriers, so it cannot tell you where a Thai line might be blocked.
• India: the common claim that India blocks WiFi Calling refers to Indian SIMs not getting WiFi Calling while roaming abroad, not to a ban on Thai SIMs used inside India.

In practice the network matters more than the country. VoWiFi needs UDP ports 500 and 4500 open to build its tunnel to the ePDG. Some public, airport or captive-portal Wi-Fi blocks them, so the WiFi Calling indicator never appears even though web pages load. True itself warns that some free Wi-Fi will not work and suggests trying another network.

How do you prepare WiFi Calling before you fly?

Do all of this while you are still in Thailand. True states plainly that WiFi Calling must be switched on in Thailand and not turned off; if you forget and only notice abroad, you may not be able to fix it without the call centre.

1. 1Update software and carrier settingsiPhone: Settings > General > About; if a new carrier settings update exists, a prompt appears. Android: run a system update from Software update. AIS notes that iPhone WiFi Calling depends on a supported carrier settings version.
2. 2Turn on WiFi Calling for the Thai lineiPhone (iOS 18): Settings > Cellular (or Mobile Service) > pick the Thai line > Wi-Fi Calling > Wi-Fi Calling on This iPhone. On iOS 26 it sits in the same section, though labels may differ slightly. Samsung (One UI 6–8): Phone app > ⋮ > Settings > Wi-Fi calling, or Settings > Connections > Wi-Fi Calling. Pixel (Android 14–16): Settings > Network & internet > SIMs > pick the SIM > Wi-Fi calling. AIS on Android: also dial *399*1#.
3. 3Set it to Wi-Fi PreferredOn Android phones that offer a mode, pick Wi-Fi Preferred, as True recommends. Cellular Preferred makes the phone try the mobile network first, which abroad means roaming.
4. 4Rehearse at home in Airplane ModeTurn on Airplane Mode, then switch Wi-Fi back on by itself. Wait for the WiFi Calling indicator (on iPhone, Control Center shows Wi-Fi next to the carrier name), call another Thai number, have someone call you back, and request one OTP. If all three work, you are ready.
5. 5Check your line status and roamingThe line must not be suspended. On prepaid, top up and extend validity to cover the whole trip. Check in your carrier's app whether roaming is active on the number. If it is and you do not want it, at least turn off data roaming, and understand that any call that does not come through WiFi Calling may be billed as roaming.
6. 6Install your data eSIM before you leaveIf you are using a data eSIM for the trip, scan its QR code and install it while you still have internet in Thailand, then leave that line off until you land, so you are not hunting for airport Wi-Fi just to get online.

Can you use WiFi Calling together with a travel data eSIM?

Most travel eSIMs, including esimonline's, are data-only and have no phone number. Calls still go through your Thai number via WiFi Calling. There are two ways to set this up, depending on whether you want certainty or convenience.

Setup A: Airplane Mode plus Wi-Fi (safest)

Keep Airplane Mode on for the whole trip and switch only Wi-Fi back on. This is what AIS and True recommend, and you cannot be charged roaming because the Thai line never touches a foreign network. The downside is that Airplane Mode also switches off the data eSIM, so once you leave the hotel you have no internet and cannot take calls until you find Wi-Fi again.

Setup B: dual SIM with data from the eSIM (convenient, test first)

Turn Airplane Mode off, make the eSIM your cellular data line, turn off data roaming on the Thai line, and let the Thai line's WiFi Calling ride on the eSIM's data. Technically this can work, because VoWiFi only needs an internet path to the ePDG, and Apple states that on a dual-SIM iPhone you can answer calls on your other number if that number's carrier supports Wi-Fi Calling. Thai carriers, however, have no official page confirming this setup. Pantip users report it working reliably on iPhone with AIS and dtac, not working with True, and on Samsung usually needing a local (non-roaming) data SIM to stay stable.

If you go with Setup B, test it on day one: eSIM on, Wi-Fi off, and check whether the Thai line shows the WiFi Calling indicator. Call someone at home, have them call you back, and check your carrier app the next day for any roaming charges. On iPhone there is also an Allow Cellular Data Switching option, but Apple notes it does not work while the data line is roaming.

Set up dual SIM correctly before you travel

WiFi Calling not working abroad: what should you check?

1. Check whether the WiFi Calling indicator is showing. If not, do not dial yet; the call may go out over roaming.
2. Open a web page to confirm you have got through the Wi-Fi login page; some hotel networks connect but still wait for you to accept terms.
3. Try another network, such as a hotspot from a second phone with a data eSIM, since some Wi-Fi blocks UDP ports 500/4500.
4. Turn off any VPN for a moment; some VPNs stop the tunnel to the ePDG from forming.
5. Toggle WiFi Calling off and on only if you know it was activated successfully in Thailand; on True/dtac, do not leave it switched off.
6. Restart the phone, then set Airplane Mode plus Wi-Fi again.
7. If it still fails, message your carrier through its app to check whether the line is suspended or not provisioned for WiFi Calling.

On emergency calls: Apple says iPhone uses the cellular network for emergency calls when it is available, and only might use WiFi Calling when there is no cellular service. A Thai line's WiFi Calling routes back to the Thai network, so do not rely on it to reach the local emergency number. Turn off Airplane Mode and dial the local emergency number instead.

WiFi Calling not working: step-by-step fixes

WiFi Calling vs roaming vs free calling apps: which makes more sense?

For friends and family who already use LINE or WhatsApp, app calls work well and cost nothing per call. But apps cannot receive calls placed to a real phone number. Calls from the bank, a hospital, a delivery driver or anyone who only has your number need the Thai line, and that is where WiFi Calling fits. Voice roaming suits people who must be reachable at all times regardless of internet, but you pay the carrier's roaming rates to answer and to call.

Compare Thai carrier roaming with an eSIM