Does Wi-Fi Calling use data? How much per minute, and do you need Wi-Fi the whole time

Does Wi-Fi Calling use data?

Yes. Wi-Fi Calling sends your voice as data over the internet of the Wi-Fi network you are connected to, but it does not take anything from your Thai line's mobile data, and the call itself is still billed under that line's normal calling plan.

So the question has two separate parts. The first is whose data the call uses. The answer is the data of whatever Wi-Fi you are on: your home broadband, the hotel network, or a hotspot shared from another phone. The second is what the call costs, and that has nothing to do with data. True-dtac's help page says Wi-Fi Calling is charged the same way as a normal phone call at your current package rate, so outgoing calls use your package minutes or prepaid balance, not your data allowance.

Under the hood this is the 3GPP VoWiFi standard. The phone builds an encrypted IPsec tunnel across the internet to a carrier gateway called the ePDG (Evolved Packet Data Gateway), then registers with the same IMS core that handles VoLTE. Every word you say travels as data packets over that Wi-Fi connection, in both directions.

Start here: what Wi-Fi Calling is and how it works

How much data does Wi-Fi Calling use per minute?

A voice call over Wi-Fi Calling uses roughly 0.5–1 MB per minute, counting both what you send and what you receive. Treat this as an estimate. No Thai carrier publishes an official figure, and 3GPP does not define one either, because the real number depends on the codec the phone and network agree on, the connection quality and how much of the call is silence.

Where the number comes from: the AMR-WB and EVS codecs

Voice on VoLTE and Wi-Fi Calling is compressed by one of two main codecs. The older one, AMR-WB (the original HD Voice codec), has nine modes from 6.60 to 23.85 kbit/s. The newer one, EVS, is the codec 3GPP specified for VoLTE and VoNR; it runs from about 5.9 up to 128 kbit/s, with everyday calls typically sitting around 13.2–24.4 kbit/s. Those rates cover only the compressed speech itself, not the packet headers around it.

What makes Wi-Fi Calling use more than the codec rate is overhead. Speech is sent in a packet every 20 milliseconds, which is 50 packets a second, and each packet carries about 40 bytes of IP, UDP and RTP headers. Because Wi-Fi Calling travels inside an IPsec tunnel to the ePDG, the tunnel adds another layer of headers on top. Our rough calculation puts one direction at about 40–60 kbit/s while someone is talking. If both sides sent continuously for a full minute, that would come to about 0.6–0.9 MB per minute. In practice the phone sends far less during silence (discontinuous transmission, DTX), and in a normal conversation each side is quiet for a good part of the time, so real calls usually land lower.

Other published figures line up with this. PingMe says a Wi-Fi call uses about 1 MB per minute. Verizon's FAQ says voice calling uses about 1–5 MB, without making clear whether that is per minute or per call. For planning, 1 MB per minute is a sensible working figure, and if the connection you are using has a very small data cap, budget up to 5 MB per minute to be safe.

To put that in perspective: calling home for 20 minutes a day on a 7-day trip adds up to roughly 140 MB at 1 MB per minute, less than a handful of short videos. The practical problem with Wi-Fi Calling is rarely the amount of data. It is usually how stable the Wi-Fi is.

Does Wi-Fi Calling use your mobile data? What happens if Wi-Fi drops

While the phone is on a Wi-Fi Calling call, all the voice data rides on Wi-Fi and nothing is taken from your Thai line's mobile data package. The key point is that Wi-Fi Calling is not a call over mobile data. If the phone has no Wi-Fi, the call goes over the cellular network as an ordinary call (VoLTE, or older 2G/3G depending on the carrier and area), and that is charged as a phone call under your plan, not as data.

In Thailand, if you walk out of Wi-Fi range mid-call, a supporting phone will try to hand the call over to VoLTE where the carrier's network allows it. Abroad with Airplane Mode on, there is no cellular network to hand over to, so the call drops as soon as Wi-Fi goes. If Airplane Mode is off abroad, the call can end up on the roaming network instead, and AIS warns that this is charged at normal voice roaming rates.

Wi-Fi Preferred versus Cellular Preferred

Many Android phones let you choose whether Wi-Fi or the mobile network comes first. True-dtac recommends Wi-Fi Preferred so the phone uses Wi-Fi whenever it is connected. With the mobile network set as preferred, the phone only uses Wi-Fi Calling when the cellular signal is weak. That does not touch your mobile data either, because calls on the cellular side are ordinary calls, but abroad without Airplane Mode it can push calls onto roaming. iPhone has no such option on the Wi-Fi Calling screen; the phone decides for you.

Does Wi-Fi Calling use data while idle?

When you are not on a call, the phone still keeps its IMS registration and IPsec tunnel alive by sending small packets now and then. The amount is tiny next to anything else you do online, but we could not find an official figure from a carrier or phone maker, so we are not putting a number on it. If you are on a capped connection, check the data counter on whatever is providing the Wi-Fi after a day and you will see your own real figure.

Do you need to stay on Wi-Fi all the time to receive calls?

Yes, if Wi-Fi Calling is your only way to receive calls, which is the usual setup abroad. AIS and True-dtac both tell you to turn on Airplane Mode and then switch Wi-Fi back on. Done that way, the phone has no cellular connection at all, so calls to your Thai number can only reach you while the phone is on Wi-Fi and registered for Wi-Fi Calling.

While you are off Wi-Fi, for example after leaving the hotel, on a bus or walking around, callers cannot reach you, and the call is handled by your carrier's settings, such as voicemail or a not-reachable message. Texts that can travel over IMS arrive once the phone is back on Wi-Fi. In Thailand without Airplane Mode, Wi-Fi Calling is only an extra path, and the phone keeps receiving calls over the mobile network as usual.

What kind of Wi-Fi works with Wi-Fi Calling

• It must actually reach the internet. On hotel or airport Wi-Fi with a sign-in web page (a captive portal), finish signing in first, or the phone will join the Wi-Fi but Wi-Fi Calling will not come up.
• It must not block UDP ports 500 and 4500, which set up the IKEv2/IPsec tunnel to the ePDG. Some office networks and public hotspots close them. True-dtac itself warns that free Wi-Fi or home Wi-Fi in some countries may not support Wi-Fi Calling, and suggests trying another network.
• It does not need to be fast, but it must be steady. A voice call needs only tens of kbit/s, but Wi-Fi with high latency or frequent dropouts makes audio break up or calls drop. AIS also says call quality depends on the quality of the Wi-Fi signal.
• A hotspot from another phone works. True-dtac states plainly that you can connect to Wi-Fi from a phone that is sharing its hotspot.

Step by step: using Wi-Fi Calling abroad

Can you use Wi-Fi Calling on a hotspot from another phone?

Yes. To the phone that joins the hotspot, it is just another Wi-Fi network; the phone neither knows nor cares whether the internet behind it is home broadband or another phone's mobile data. True-dtac includes this option in its own steps for using Wi-Fi Calling abroad. The thing to know is that the call's data, both upload and download, comes out of the allowance of the phone sharing the hotspot.

• The phone sharing the hotspot: abroad, if it shares data from a Thai SIM, that is data roaming, so check your roaming package first. If it shares a travel eSIM or local SIM, the data comes out of that plan.
• Some plans limit or do not allow hotspot sharing, so read the terms of the plan you will share from before you travel.
• Keep the two phones close together. A phone hotspot has limited range, and some phones switch the hotspot off by themselves after a while with nothing connected. If you need to be reachable all day, make sure the sharing phone is not turning its hotspot off.
• Sharing a hotspot drains the sharing phone's battery faster than normal, so carry a power bank if you run it all day.

Can a travel eSIM provide the internet for Wi-Fi Calling?

Yes, and the most certain way is with two phones. First, be clear about roles. A travel eSIM such as the ones esimonline sells is data-only and has no phone number. The Wi-Fi Calling you are using belongs to your Thai number (AIS, True or dtac). The travel eSIM only supplies the internet connection; it does not itself make your Thai number callable.

Option 1: two phones, one running the travel eSIM as a hotspot

1. 1Turn on Wi-Fi Calling for your Thai number while still in ThailandTrue-dtac says Wi-Fi Calling has to be switched on while you are in Thailand and left on before you travel. On iPhone it is under Settings > Cellular (Mobile Data in some regions) > Wi-Fi Calling. On Android the menu name varies by model and carrier; on Samsung it is in the Phone app > three-dot menu > Settings > Wi-Fi Calling. AIS customers on Android register by dialling *399*1#.
2. 2Install the travel eSIM on the second phone and turn on its hotspotThe second device can be an old phone, a tablet that takes a SIM, or a pocket Wi-Fi router. Turn on Personal Hotspot (iPhone) or Mobile Hotspot (Android) and set a password.
3. 3On the phone with your Thai number: Airplane Mode on, then Wi-Fi onThis follows AIS and True-dtac's advice so calls cannot slip onto the roaming network. Then join the hotspot from the second phone.
4. 4Check for the Wi-Fi Calling indicator before callingOn iPhone, open Control Center and look for Wi-Fi next to the carrier name, as Apple describes. On Android, look for a phone icon with Wi-Fi waves or the carrier name followed by Wi-Fi Calling. Then make a short test call to someone you know.

Option 2: one dual-SIM phone, with the Thai line using the travel eSIM's data

A phone cannot share a hotspot with itself, but a dual-SIM iPhone has a mechanism that lets one line use the other line's data. Apple's Dual SIM article explains that with Allow Cellular Data Switching turned on, the status bar can show the second line using the first line's cellular data and having Wi-Fi Calling enabled. In other words, iPhone can technically carry one line's Wi-Fi Calling over the other line's data.

Whether that works with your Thai number depends on whether your carrier lets Wi-Fi Calling register over another SIM's data. AIS and True-dtac do not cover this on the official pages we opened, and user reports in Thai forums differ by carrier. Some Android brands have a feature called Backup calling, but its conditions vary by model and firmware region, and we found no official document confirming it works when the data SIM is roaming. If you want to rely on it, test before you travel: turn Wi-Fi off and see whether your Thai line still shows the Wi-Fi Calling indicator. Keep the two-phone setup or hotel Wi-Fi as your fallback.

Dual SIM settings that keep your Thai line off data roaming

How much extra data to budget for Wi-Fi Calling

A simple rule: the minutes you expect to talk over the whole trip × 1 MB, then double it if the connection may be patchy. For example, 150 minutes of calls means setting aside roughly 150–300 MB. Video calls are a different scale: Verizon puts one minute at 6–30 MB, so if you plan to video call often, look at a larger or unlimited plan.

See data-only travel eSIMs you can share as a hotspot

Comparing internet sources for Wi-Fi Calling: whose data gets used

How to check how much data Wi-Fi Calling used

The phone making the call does not show Wi-Fi Calling data as a clear separate figure, because it runs over Wi-Fi and the phone's data statistics mostly count mobile data. The reliable way to get a real number is to look at whatever is supplying the internet.

1. Hotspot from another iPhone: on the sharing phone, go to Settings > Cellular and scroll to Personal Hotspot, which shows what connected devices used. Reset the statistics before a call to see that call's figure clearly.
2. Hotspot from Android: on the sharing phone, open the data usage screen (the name varies by brand, for example Settings > Connections > Data usage on Samsung, or Settings > Network & internet on Pixel) and look at the hotspot or tethering entry.
3. Travel eSIM: check the remaining balance in the eSIM provider's app or web page before and after a call.
4. Home Wi-Fi or a pocket Wi-Fi router: check the statistics in the router's admin page or the provider's app.

If you see much more than about 1 MB per minute, check whether something else was using the connection at the same time, such as photos syncing to the cloud, apps updating, or the camera being switched on and turning the call into a video call.

Wi-Fi Calling versus LINE or WhatsApp calls: is the data use different?

Both send your voice as data over the internet, so voice calls land in the same general range, from a few hundred KB to around 1 MB a minute, depending on each app's codec and the connection. The important difference is not data but who you can reach and what you pay.

For detailed figures on chat apps, see our articles on LINE and WhatsApp data use and on video calls abroad, linked at the end of this page.

How to keep Wi-Fi Calling light on data and avoid missed calls

• Test before you leave: Airplane Mode on, join your home Wi-Fi, and call someone you know. If the Wi-Fi Calling indicator does not appear, you can fix it while still in Thailand.
• If the hotspot has a data cap, turn off photo sync and automatic app updates on the phone with your Thai number, because it sees the hotspot as ordinary Wi-Fi and may use data heavily. On iPhone you can turn on Low Data Mode for that network under Settings > Wi-Fi > tap (i) next to the network name.
• Avoid video calls on a small data allowance; voice uses many times less data than video.
• If you are waiting for an important call, such as a voice OTP or a call from your bank, stay somewhere with steady Wi-Fi or keep the hotspot running during that window.
• With no Wi-Fi and no second device, switching Airplane Mode off to take a call means taking it on roaming, so check your Thai line's roaming charges first.

Does Wi-Fi Calling cost money? How calls are billed