dtac WiFi Calling: how to turn it on, set it up and fix it when it does not work

What is dtac WiFi Calling, and does it still work after the True merger?

Yes. dtac WiFi Calling lets you make and receive calls on your dtac number over a Wi-Fi connection instead of the mobile network. You turn it on in the settings of a supported iPhone or Android phone; no extra app is needed.

After dtac and True combined into True Corporation in 2023, dtac's old WiFi Calling page (dtac.co.th/en/network/wifi-calling.html) now redirects to true.th. The official guide is the shared page titled 'How to set up Wi-Fi Calling | True-dtac', which covers customers of both brands. Apple's Asia-Pacific carrier list still names dtac as its own entry, supporting Wi-Fi Calling and VoLTE on iPhone.

Technically, WiFi Calling is VoWiFi as defined by 3GPP. The phone builds an encrypted IPsec tunnel over the internet to a carrier gateway called the ePDG, then registers with the same IMS core that handles VoLTE. The call is still your dtac number: the other person sees your normal caller ID, and it is billed on your normal package. That is the difference from LINE or WhatsApp calls, which need the other person to use the same app.

Start with the basics: what is WiFi Calling

Who can use dtac WiFi Calling? Does it work on postpaid and prepaid?

The True-dtac guide says the service is open to both postpaid and prepaid customers, works in Thailand and abroad, and is billed at your normal package rates. These are the conditions you need to meet:

• The SIM must be active: not suspended, not expired, and a prepaid number must still have validity days left.
• Prepaid customers have to take the SIM card and their original national ID card to a True or dtac shop to confirm the service request, as the regulator (NBTC) requires. Until that is done, the toggle may switch on but calls will not go over Wi-Fi.
• A physical dtac SIM or a dtac eSIM both work, as long as that number is installed in the phone you call from.
• The phone must support WiFi Calling on the dtac network and run the latest software.
• The first switch-on needs dtac mobile signal, which means doing it while you are in Thailand.

Which phones support dtac WiFi Calling?

True-dtac does not publish a single current model list; the guide only says the phone must support the feature and run the latest software. Old guides from the dtac WiFi Calling app era limited it to a handful of models such as the Samsung Galaxy S6 and iPhone 5s to 6s, and those lists are no longer a useful reference. A more reliable check is the phone's own menu, as in this table.

Grey-import phones often lack the menu because WiFi Calling is a carrier-provisioned feature: the phone needs carrier configuration that matches the dtac SIM. On Samsung this is tied to the CSC region code, so a phone built for another country may not recognise dtac's VoWiFi settings at all. If you are buying a phone and want this feature, choose a Thai-market unit.

How do you turn on dtac WiFi Calling on iPhone?

1. 1Update iOS and carrier settingsGo to Settings > General > Software Update, then open Settings > General > About and wait a few seconds. If a carrier settings update pops up, tap Update.
2. 2Open the Wi-Fi Calling menuGo to Settings > Cellular (called Mobile Service or Mobile Data on some phones) > Wi-Fi Calling. On a dual-SIM iPhone, tap the dtac line first and the option appears inside it. Older iOS versions put it at Settings > Phone > Wi-Fi Calling. If you cannot find it, type 'Wi-Fi Calling' into the search bar at the top of Settings.
3. 3Switch it on and confirmTurn on 'Wi-Fi Calling on This iPhone' and tap Enable. If the phone asks for an address for emergency services, enter your real address.
4. 4Test with Airplane ModeTurn on Airplane Mode, then turn Wi-Fi back on and connect. Open Control Center and check that 'Wi-Fi' appears after the carrier name at the top. Then call a Thai number; if it connects, WiFi Calling is working.

Note: the True-dtac guide gives the iPhone path as Settings > Connections, which does not match the real iOS menu. Apple's documented path is Settings > Cellular > Wi-Fi Calling. Apple has not published an article confirming the location on iOS 26; if the menu has moved on your phone, use the search bar in Settings.

How do you turn on dtac WiFi Calling on Android and Samsung?

1. 1Update the systemGo to Settings > Software update and install the latest version, because carrier VoWiFi settings often arrive with system updates.
2. 2Open the Wi-Fi Calling menuSamsung One UI 6 to 8: Settings > Connections > Wi-Fi Calling, or Phone app > ⋮ > Settings > Wi-Fi Calling. On Pixel and stock Android 14 to 16 it is usually Settings > Network & internet > SIMs > your dtac line > Wi-Fi calling. Other brands may put it under SIM cards & mobile networks.
3. 3Enable it for the dtac line and pick Wi-Fi preferredSwitch it on for the dtac number (physical SIM or eSIM) and set the calling preference to 'Wi-Fi preferred', as True-dtac recommends. With 'Mobile network preferred', the phone only uses Wi-Fi when there is no signal.
4. 4Restart and look for the iconRestart the phone once. When it is active, you will see a phone-with-Wi-Fi-waves icon in the status bar, or 'Wi-Fi Calling' or 'VoWiFi' in the notification shade.

Early dtac guides told Samsung owners to dial a USSD code to register before the menu would appear. That code belongs to the era when the service was tied to specific models, and the current True-dtac guide no longer asks you to dial anything. If the menu does not appear, contact 1678 rather than trying codes from old web pages.

How can you tell dtac WiFi Calling is really working?

A switched-on toggle does not mean calls are going over Wi-Fi. What matters is that the phone has registered with IMS over Wi-Fi. Check these:

• iPhone: open Control Center and look for 'Wi-Fi' after the carrier name, as Apple describes.
• Android: look for the WiFi Calling icon in the status bar, or dial *#*#4636#*#*, open Phone info > ⋮ > IMS service status and check that WFC shows as registered. This is a diagnostic menu, not an official Google feature, and some brands disable it.
• Real test: turn on Airplane Mode, connect Wi-Fi, call a Thai number, then have someone call you. Both directions must work.
• Send one SMS to a Thai number while in Airplane Mode to check that messages also go over Wi-Fi.

dtac WiFi Calling not working or will not switch on: how do you fix it?

The complaint dtac users post most often on Pantip is that the iPhone toggle will not stay on, especially when they are already abroad. This table matches common symptoms with likely causes and fixes.

If it still fails, work through the order Apple recommends, which applies to most Android phones too: confirm the carrier supports it, update the software, turn WiFi Calling off and on, restart, try a different Wi-Fi network, and finally reset network settings (iPhone: Settings > General > Transfer or Reset iPhone > Reset > Reset Network Settings). That reset erases every saved Wi-Fi password. If none of this works, the problem is usually on the carrier side, so contact 1678.

Full troubleshooting guide: WiFi Calling not working

How do you use dtac WiFi Calling abroad without roaming charges?

The main benefit for travellers is taking calls and calling Thailand on your usual dtac number over Wi-Fi, without going through a roaming network. True-dtac gives these steps:

1. Before leaving Thailand: turn WiFi Calling on, make a successful test call, and leave the switch on for the whole trip.
2. Dial ##002# and press call to cancel call forwarding to voicemail, which prevents unexpected charges.
3. Turn on Airplane Mode before landing and keep it on, so the dtac line never attaches to a roaming network.
4. Turn on Wi-Fi only, connect, and wait for the WiFi Calling indicator before every call.
5. If public Wi-Fi does not work, change networks or use a personal hotspot from another phone.

What about a travel eSIM? esimonline's eSIMs, like most travel eSIMs, are data-only with no phone number, so calls to your dtac number still depend on dtac's own WiFi Calling. The most reliable setup is to run a hotspot from a second phone that has the eSIM and connect the dtac phone to it. The other option is both lines in one phone: make the eSIM the cellular data line, turn off roaming on the dtac line, and let WiFi Calling ride on the eSIM's data. Apple says that on a dual-SIM iPhone you can answer calls on your other number if that number's carrier supports Wi-Fi Calling, but True-dtac has no official page confirming this setup. Pantip users report that dtac lines appear to work this way without a firm conclusion, so test it before you rely on it.

Prepare WiFi Calling before an overseas trip

Does dtac WiFi Calling cost money, and how are calls billed?

There is no separate sign-up fee, but calls are not free. True-dtac says billing is the same as a normal phone call at your current package rate, so the per-minute cost depends on your plan; check it in the carrier's app or ask 1678. As for data, the figure usually quoted is about 0.5 to 1 MB per minute of voice, which is an estimate rather than an official number.

Contacting dtac on 1678 about WiFi Calling: what should you have ready?

1678 is dtac's call centre number, which you can dial directly from a dtac line. If you are abroad without working WiFi Calling, use chat in the dtac app or dtac's LINE account instead, because calling the call centre over roaming may be charged. Have these details ready so the agent can check quickly:

• The dtac number with the problem, and whether it is postpaid or prepaid.
• Phone brand, model and software version, and whether it is a Thai-market unit or an import.
• The exact symptom: no menu, toggle flips back, or on but no Wi-Fi indicator.
• What you have already tried: updating, restarting, changing Wi-Fi, resetting network settings.
• For a prepaid line, ask whether the in-shop service confirmation has been recorded.

Ask clearly for them to check whether VoWiFi, or WiFi Calling, is provisioned on your number. Some problems cannot be fixed on the phone at all; the carrier's system has to enable the feature for that line first.

See data eSIMs for travel