WiFi Calling not working? Check the Wi-Fi, SIM, phone and settings step by step

Why does WiFi Calling fail even when it is switched on?

Because the WiFi Calling switch only gives the phone permission to try. An actual call needs three more things: Wi-Fi that really reaches the internet, a working encrypted tunnel from the phone to your carrier's network, and a SIM that successfully registers for voice over Wi-Fi. If any one of these fails, the WiFi Calling indicator does not appear, and the call either fails or falls back to the mobile network.

Technically, WiFi Calling is VoWiFi as defined by 3GPP. The phone uses Wi-Fi to reach a carrier gateway called the ePDG (Evolved Packet Data Gateway), proves who it is with keys stored on the SIM using IKEv2, and then builds an IPsec tunnel. All voice and call signalling runs inside that tunnel to IMS, the same core that VoLTE uses. Setting up the tunnel uses UDP port 500 and the traffic then flows over UDP port 4500. On any network that blocks those two ports, WiFi Calling will not work, even though web pages and LINE work normally.

The table below maps common symptoms to the most likely cause and the first thing to try. Use it as a starting point, then read the matching section below.

No WiFi Calling menu at all? Read the missing-menu guide

How can you tell whether WiFi Calling is actually active?

Check the status before fixing anything, because “calls don't work” comes in two kinds that need different fixes. In the first, WiFi Calling never registered at all. In the second, it registered but the voice traffic does not get through. Whether the indicator appears tells you straight away which kind you have.

• iPhone: Apple says that when WiFi Calling is working you will see “Wi-Fi” in the status bar next to the carrier name when you open Control Center, for example “AIS Wi-Fi”.
• Android: Google says you will see “Wi-Fi calling” or “Internet Call” on the notification screen once it is connected. Many Samsung phones also show a phone-and-Wi-Fi icon in the status bar.
• Android, in detail: on many models, typing *#*#4636#*#* in the Phone app opens a testing menu. Tap the three-dot menu, then IMS Service Status, to see whether IMS is registered and whether VoWiFi is available. This menu is not documented by Google and some brands disable it.
• A clear test: turn on Airplane Mode, then switch only Wi-Fi back on. If you can still make and receive calls, they are definitely going over WiFi Calling, because the phone has no mobile signal left to use. True-dtac recommends this same test on its setup page.

If the indicator is missing, work through the sections on Wi-Fi, routers and VPNs, and the SIM. If it shows but calls go silent or drop, go to the sections on Wi-Fi quality and dropped calls. Do not start by resetting the phone: resetting network settings also deletes every saved Wi-Fi password.

The Wi-Fi is connected, so why won't WiFi Calling work?

“Connected to Wi-Fi” does not mean “on the internet”. Most public Wi-Fi in hotels, airports, malls and cafés uses a login or terms page (a captive portal) before it lets traffic out. Until you accept it, the phone shows Wi-Fi as connected, but it cannot build the tunnel to the ePDG, so WiFi Calling never appears. The easiest check is to open any website in the browser. If it jumps to a login page, complete it, then wait a moment for the indicator to appear.

The second issue is Wi-Fi quality. A call does not use much data, but it needs a steady connection. If the signal is weak, many people are sharing the network, or the connection keeps stalling, the audio breaks up or the call drops. AIS WiFi Calling guides note that voice quality depends on the Wi-Fi you are using. Play a short video or run a speed test: if video stutters, calls will usually struggle too.

To tell whether the problem is that particular Wi-Fi network or the phone, turn on a hotspot on another phone and connect to it. If WiFi Calling works on the hotspot but not on the original Wi-Fi, the fault lies with that network, not with the SIM or the phone. True-dtac suggests the same approach, trying home Wi-Fi, public Wi-Fi and a hotspot from another phone, and states plainly that some free Wi-Fi abroad does not support WiFi Calling.

Can a router, VPN or hotel Wi-Fi block WiFi Calling?

Yes, and it is the cause people overlook most, because everything else on the internet works fine. WiFi Calling does not travel like ordinary web traffic; it goes through an IPsec tunnel on UDP ports 500 and 4500. Networks with strict firewalls, such as office, university or hospital Wi-Fi and the guest Wi-Fi in some hotels, often close ports that are not used for browsing, so WiFi Calling fails on that network only.

What to check on a home or office router

1. 1Restart the router firstUnplug the router for about half a minute and plug it back in. A router that has been running for a long time can hold stale connection (NAT) entries that keep breaking the tunnel to the ePDG.
2. 2Make sure the firewall lets UDP 500 and 4500 outIn the router settings, check that outbound firewall rules do not block UDP 500 and 4500, and if there is an IPsec passthrough option, turn it on. Typical home routers already allow this; the problem shows up more on business-grade firewalls.
3. 3Try turning off SIP ALGMany routers have a SIP ALG feature that tries to rewrite internet call traffic. Network admin forums often report it interfering with WiFi Calling. If your router has this option, try turning it off and restarting. This comes from user experience, not from official router-maker documentation.
4. 4On office Wi-Fi, ask ITTell IT you need WiFi Calling and ask them to allow outbound UDP 500 and 4500 to mobile carrier gateways. Many network admins allow the *.pub.3gppnetwork.org domain, the naming pattern carriers use for their ePDGs.

Does a VPN really stop WiFi Calling?

Often, yes. A VPN wraps all of the phone's traffic and sends it out through the VPN server, so the WiFi Calling tunnel has to run inside another tunnel. Some VPN apps handle UDP poorly, and some carriers do not accept ePDG connections coming from VPN provider IP addresses. Thai troubleshooting guides list a VPN as a common cause and advise turning it off and trying again. If the indicator appears once the VPN is off, stop the VPN from connecting automatically, or use split tunnelling if the app offers it.

What if WiFi Calling won't work on hotel Wi-Fi?

1. Open a browser and finish the login or terms page. Some hotels ask you to log in again every day or when you move floors.
2. Forget the network and rejoin. If the hotel has several network names, try another one; room and lobby networks may have different firewall rules.
3. Ask the front desk whether the Wi-Fi blocks internet calls or VPNs. If it does, no phone setting will make WiFi Calling work on that network.
4. A workaround that often helps is a hotspot from a second phone with a local data eSIM, or the data eSIM in the same phone in a dual-SIM setup, tested before you rely on it.

Do some countries stop WiFi Calling from working?

It can happen, but there is no official country list from GSMA or the Thai carriers. A 2024 study, Why E.T. Can't Phone Home, which surveyed operators worldwide, found that a share of operators block VoWiFi connections based on the IP address of the country or continent the user is in, notably some in Europe and Asia, with India the largest single contributor. AIS, True and dtac were not covered by that study, so there is no confirmed data on which countries block Thai numbers.

Another thing that often gets mixed in is countries that restrict internet calling apps, such as the UAE, which blocks calls in consumer apps like WhatsApp and FaceTime Audio, and China, which blocks many foreign apps. That is a different matter from WiFi Calling, which is a service run by the mobile carrier itself, so traveller reports are mixed: some people get it working and some do not, depending on the Wi-Fi they use. For India, the confirmed restriction is that Indian carriers limit their own customers' VoWiFi while roaming, not that foreign numbers are blocked inside India.

In practice, if WiFi Calling fails on every network you try in a country, hotel Wi-Fi, café Wi-Fi and a hotspot from a data eSIM alike, suspect network-level or country-level blocking and prepare a fallback, such as an internet calling app that works there, or switching on roaming only when needed and knowing the rates in advance.

Using WiFi Calling abroad: preparation and costs

Could the SIM or the number be why WiFi Calling won't work?

Yes. If you have tried several Wi-Fi networks and the indicator never appears, the problem is probably the SIM or the account. WiFi Calling has to be enabled for that number by the carrier, and the SIM has to register with IMS. True-dtac lists the basic conditions: a SIM or eSIM in the phone, SIM status Active and not suspended, a supported phone on the latest software, and WiFi Calling switched on.

• Unpaid or suspended number: if the line cannot make normal calls, WiFi Calling will not work either, because it uses the same number and account. Check the carrier's app first.
• Activate before you leave Thailand: True-dtac says WiFi Calling must first be switched on while you are in Thailand and should not be turned off before you travel. If you forgot and are already abroad, True-dtac's help page says you need mobile signal and international calling enabled on the SIM to try activating it.
• AIS on Android: AIS registers the service when you dial *399*1#. If you never registered, the switch on the phone may turn on but calls will not go through. On iPhone, AIS enables it through the carrier settings with no code to dial.
• Outdated carrier settings on iPhone: go to Settings > General > About and wait a few seconds. If a carrier settings update is available, a prompt appears asking you to update.
• Wrong line on a dual-SIM phone: on iPhone you pick the number first, then its WiFi Calling switch appears. Android also sets it per SIM. Make sure it is on for your Thai number, not for a data-only eSIM that has no number.
• Android switching it off by itself: Google says that if the phone detects problems it may turn WiFi Calling off automatically, and you may need to restart or contact your carrier to reactivate it. If the switch you turned on is suddenly off, this may be why.

If you use a data-only travel eSIM, such as esimonline's, remember it has no phone number, so WiFi Calling always runs on your Thai number. Whether your Thai line's WiFi Calling can ride on the eSIM's cellular data instead of Wi-Fi is not confirmed on any official Thai carrier page. Apple only says that on a dual-SIM iPhone you can answer calls on your other number during a call if that number's carrier supports Wi-Fi Calling, and that Allow Cellular Data Switching does not work while the data line is roaming. Test it yourself on the first day of the trip.

Set up dual SIM so your Thai number and data eSIM work together

Step-by-step checklist to fix WiFi Calling

The steps run from quick and harmless to the ones that change settings. Apple suggests waiting about two minutes after each step, because the phone needs time to register again. Menu names can differ by model, software version and carrier.

1. 11. Confirm WiFi Calling is really oniPhone: Apple's path is Settings > Cellular (or Mobile Data) > Wi-Fi Calling, then turn on Wi-Fi Calling on This iPhone; on some iOS versions and in Thai carrier guides it sits under Settings > Phone. Samsung: Settings > Connections > Wi-Fi Calling, or Phone app > three-dot menu > Settings. Pixel and stock Android: Settings > Network & internet > SIMs > choose the SIM > Wi-Fi calling.
2. 22. Check the Wi-Fi actually reaches the internetOpen a fresh web page. If a login page appears, complete it. If pages load very slowly, move closer to the router or switch networks.
3. 33. Turn off VPNs and traffic-filtering appsTemporarily turn off any VPN, VPN-style ad blocker or installed DNS profile, then wait to see whether the indicator appears. Samsung also suggests uninstalling recently installed apps if you suspect they interfere.
4. 44. Turn on Airplane Mode, then Wi-Fi againLeave it for about half a minute and switch only Wi-Fi back on. The phone starts registering from scratch. Abroad, this also stops calls from slipping onto roaming.
5. 55. Restart the phoneApple, Samsung and True-dtac all include this step, because it clears a stuck IMS registration.
6. 66. Try another Wi-Fi network or a hotspotIf another network works, the original network is the problem, so go back to the login page, firewall and router checks. If no network works, suspect the SIM, the account or country-level blocking.
7. 77. Switch WiFi Calling off and onApple recommends this, but be careful if you are abroad on True or dtac: True-dtac says the first activation has to happen in Thailand, so once switched off it may be harder to turn back on.
8. 88. Update the software and carrier settingsiPhone: Settings > General > Software Update, and check for a carrier update in Settings > General > About. Samsung: Settings > Software update. Other Android: Settings > System > System update.
9. 99. Reset network settingsiPhone: Settings > General > Transfer or Reset iPhone > Reset > Reset Network Settings. Samsung: Settings > General management > Reset > Reset mobile network settings. This removes all saved Wi-Fi passwords, so note them down first.
10. 1010. Contact your carrierIf none of this works, ask your carrier to check that WiFi Calling and VoLTE are provisioned on your number and what the registration status is. Abroad, the chat in the carrier's app is usually easier than calling.

Calls connect but drop, break up or never ring: what then?

If the WiFi Calling indicator is there but call quality is poor, the cause is usually not a setting but the path the data takes during the call. A voice call needs little data, with many carrier and eSIM guides estimating roughly 0.5 to 1 MB per minute for voice, but it needs low delay and no gaps. Large downloads or video streaming on the same network during the call can make audio break up even when the headline speed looks fine.

• Drops when you walk outside: that is when Wi-Fi weakens and the phone tries to hand the call to the mobile network. Abroad with Airplane Mode on, the call has nowhere to go and drops, so stay within Wi-Fi range until you hang up.
• Choppy audio: move closer to the router, pause downloads and cloud backups during the call, and if you have several networks at home, join the strongest one.
• Outgoing works but nothing rings: check that Do Not Disturb or a Focus mode is off, that call forwarding is not set, and on a dual-SIM phone that WiFi Calling is on for the number people actually call. True-dtac also suggests dialling ##002# to cancel forwarding to voicemail, which avoids unexpected charges abroad.
• At home in Thailand with good mobile signal: some phones prefer the mobile network, so WiFi Calling rarely shows. If your phone has a Wi-Fi Preferred option, as True-dtac recommends on Android, choose it.

When should you contact AIS, True or dtac, and what should you tell them?

Contact your carrier once you have worked through the checklist, tried more than one network including a hotspot, and the WiFi Calling indicator still never appears, or if the menu was never there to begin with. These issues are usually fixed on the carrier's side, for example by provisioning the service on your number, resetting IMS registration or replacing the SIM.

• Give the phone model and software version, for example iPhone 15 on iOS 18 or Galaxy S24 on One UI 7, and say whether it was bought in Thailand or imported.
• Say whether the WiFi Calling indicator ever appears and which networks you tried, including a hotspot.
• If you are abroad, say which country you are in and whether WiFi Calling was switched on before you left Thailand.
• Common channels: AIS 1175, True 1242 and dtac 1678 from a Thai line. Abroad, chat in the myAIS app or the True-dtac app is usually easier and avoids roaming call charges.

If the carrier confirms everything is provisioned but the WiFi Calling option on the phone is missing or greyed out, the phone itself may be the issue, for example an imported phone whose firmware does not match Thai carriers. That is covered in the guide on a missing WiFi Calling menu. If you are still unsure how WiFi Calling works at all, the basics guide is the easier place to start.

What WiFi Calling is and how it works