WiFi Calling vs VoLTE: what is the difference, and which one uses Wi-Fi or the mobile network?

What is the difference between WiFi Calling and VoLTE?

The difference is the path your voice takes. WiFi Calling uses Wi-Fi to reach the internet and then enters your carrier's network, while VoLTE uses the 4G signal from your carrier's own towers. Both end up in the same system, and the person you call sees your usual number either way.

Both are packet (IP) calls that register into the same IMS (IP Multimedia Subsystem) core run by your carrier. 3GPP describes IMS as an access-independent service control architecture, which is why it can accept calls arriving over 4G, 5G or Wi-Fi. That is also why you need no extra app: the built-in Phone app handles both, and text messages can travel the same way (SMS over IP).

• WiFi Calling (VoWiFi): phone → Wi-Fi → internet → carrier's ePDG → IMS
• VoLTE: phone → 4G tower (eNodeB) → 4G core (EPC) → IMS
• VoNR: phone → 5G tower (gNodeB) → 5G standalone core → IMS
• 2G/3G call: phone → 2G/3G tower → circuit-switched switching centre, no IMS involved

Comparison table: WiFi Calling vs VoLTE vs VoNR vs 2G/3G calls

This table sums up the differences you notice as a user, not just the technology names. For travellers, the rows that matter most are 'use abroad' and 'cost'.

How do WiFi Calling, VoLTE, VoNR and 2G/3G calls work?

WiFi Calling (VoWiFi): a call inside an encrypted tunnel to your carrier

With WiFi Calling on, your phone uses the Wi-Fi it is connected to and goes across the internet to a carrier server called the ePDG (Evolved Packet Data Gateway), the security gateway for access from Wi-Fi networks the carrier does not control. The phone and the ePDG authenticate with IKEv2 and EAP-AKA, using the secret keys stored on your SIM, and then build an IPsec tunnel. All voice and messaging traffic runs inside that tunnel on to IMS. The common industry profile is GSMA IR.51, which sets the minimum feature set for voice, video and SMS over Wi-Fi.

In practice this means a Wi-Fi network that blocks UDP ports 500 and 4500 (used to set up the IKE and IPsec tunnel) will stop WiFi Calling from registering even though web pages load fine. On public Wi-Fi with a sign-in page, you have to finish signing in before the tunnel can connect.

VoLTE: calls on 4G with a lane reserved for voice

VoLTE (Voice over LTE) sends your voice as packets straight over your carrier's 4G network. Unlike Wi-Fi, the mobile network applies end-to-end quality of service (QoS) to the voice stream, so speech gets priority over other traffic. The codecs are AMR-WB and EVS, which give HD Voice. During the call the phone stays on 4G, so mobile data keeps working. On iPhone, the 'Voice & Data' option in cellular settings means, in Apple's words, voice calls and cellular data both run over LTE.

VoNR: the 5G version of VoLTE, which needs standalone 5G

3GPP describes VoNR (Voice over New Radio) as voice delivered through IMS over 5G, the 5G counterpart of VoLTE, with standardisation starting in Release 15. The catch is that VoNR needs a standalone (SA) 5G core. If the carrier runs non-standalone 5G, or has not switched VoNR on in that area, a phone showing a 5G icon drops back to VoLTE on 4G when a call starts. This is called EPS fallback. For most people, a call on a phone that says 5G is still a VoLTE call.

2G/3G calls: the old circuit-switched system being switched off

Before VoLTE, calls used the circuit-switched systems of 2G and 3G, which hold a reserved channel for the whole call. A 4G phone without VoLTE uses CSFB (Circuit-Switched Fallback): it drops from 4G to 3G or 2G whenever a call starts, so calls take longer to connect and data slows or stops during the call. The bigger problem now is that many countries have switched 2G/3G off. Google notes that visitors roaming in the US on a device without VoLTE roaming support can lose voice calling on the affected networks. If your phone or carrier still relies on 3G for calls, you may have no way to call over the mobile network in a country like that.

When does your phone use WiFi Calling and when does it use VoLTE?

You do not pick one each time. The phone decides based on signal, your settings and what your carrier allows. These are the usual cases:

• In Thailand with good 4G/5G signal: calls go over VoLTE (or VoNR where the area and phone support it), even while you are on Wi-Fi, if the phone is set to prefer the mobile network.
• Inside a building or condo with weak signal but Wi-Fi available: calls move to WiFi Calling. AIS's call-centre guide says iPhone switches to WiFi Calling on its own when the cellular signal is weak.
• Android set to 'Wi-Fi Preferred': the phone uses WiFi Calling first whenever usable Wi-Fi is there. True-dtac's setup guide tells you to pick this mode.
• Airplane Mode on, then Wi-Fi turned back on: the cellular radio is off, so WiFi Calling is the only path. This is the method AIS and True-dtac recommend abroad.
• Phone or SIM without VoLTE, or outside 4G coverage: the call drops to 3G/2G through CSFB, if those networks still exist.
• Emergency calls: Apple says iPhone uses the cellular network when it is available, and may use WiFi Calling only when cellular service is not available.

If you walk out of Wi-Fi during a WiFi Calling call, will it drop?

Not necessarily. Because WiFi Calling and VoLTE sit on the same IMS core, the standards support handing a single call over between Wi-Fi and 4G. You can start a call in your room, walk out of the condo, and the call moves to VoLTE. There are three conditions: the carrier must have this handover switched on, the phone must support it, and there must be 4G signal from your carrier where you walk to.

Abroad, that last condition is often missing. With Airplane Mode on, the cellular radio is off, so there is no network to hand over to: when the Wi-Fi goes, the call drops. If Airplane Mode is off and the phone is registered on a foreign network by roaming, the call that moves over becomes a roaming call and is charged as one. The other direction, moving from 4G onto Wi-Fi mid-call, depends on the carrier and phone; some phones wait until you hang up and use WiFi Calling for the next call.

When a VoLTE call leaves 4G coverage, carriers that still run 3G/2G use SRVCC (Single Radio Voice Call Continuity) to pass the call down to the circuit-switched network without cutting it. A VoNR call falls back to VoLTE when it leaves 5G SA coverage.

Do WiFi Calling and VoLTE cost differently, and do they use much data?

In Thailand both are charged like a normal call. True-dtac's guide says calls are billed like ordinary calls at your package rate, which means minutes come out of your package and there is no extra activation fee. What differs is whose data is used. VoLTE is your carrier's voice service, and most carriers do not take it from your mobile data allowance (UK carrier giffgaff, for example, states plainly that it does not). WiFi Calling uses data from the Wi-Fi you are on.

The data a voice call needs is small. The EVS codec runs from around 5.9 kbps upward, and AMR-WB sits between 4.75 and 23.85 kbps. Adding packet headers and the IPsec tunnel, several eSIM and calling-service guides estimate about 0.5 to 1 MB per minute. That is an estimate, not an official 3GPP or GSMA figure, and video calls use a lot more.

Abroad is where the costs really split. A call that runs over a foreign network, whether VoLTE roaming or 3G, is charged as voice roaming at your carrier's rate. WiFi Calling does not use the foreign network: True-dtac says it works in Thailand and abroad over Wi-Fi at your package rate. For AIS's charges while abroad, check AIS's own pages or call 1175, because we could not find an official page that states the rate clearly.

Read next: does WiFi Calling cost money, and how is it charged?

Abroad, should you use WiFi Calling or VoLTE?

If the goal is to call and receive calls on your Thai number without paying roaming, use WiFi Calling on your hotel's or rental's Wi-Fi. VoLTE abroad is roaming: roaming has to be on, your Thai carrier needs a VoLTE roaming agreement with the local network, and it is always charged as roaming. It is useful only when there is no Wi-Fi and you really need to call.

1. Turn WiFi Calling on while you are still in Thailand. True-dtac says it must be switched on in Thailand and left on.
2. On arrival, switch on Airplane Mode, then turn Wi-Fi back on and join your accommodation's Wi-Fi.
3. Wait for the WiFi Calling indicator before you dial (AIS says to look for the 'AIS WiFi Call' icon). On iPhone, Control Center shows 'Wi-Fi' after the carrier name.
4. When you go out and need data, use a travel eSIM or a roaming data pack, and keep roaming off on the Thai SIM if you want to avoid voice roaming charges.

With a data-only eSIM next to your Thai SIM, how do calls on your Thai number travel?

esimonline travel eSIMs are data-only and come with no phone number, so the WiFi Calling and VoLTE discussed here belong to your Thai SIM (AIS, True or dtac), not the eSIM. A common question is whether your Thai number's WiFi Calling can ride on the other line's mobile data in a dual-SIM phone. What can be verified today is that no official Apple or Samsung page confirms this works in all cases. Samsung's Backup calling feature, as described in user community reports, is reported not to work when the SIM supplying the data is roaming, which is usually the case for a travel eSIM. The dependable approach is WiFi Calling on real Wi-Fi, with the eSIM handling data during the day.

Step-by-step guide to using WiFi Calling abroad

How can you tell whether a call is using WiFi Calling or VoLTE, and where are the switches?

Menu names differ by model, carrier and OS version. The paths below are the ones confirmed on official or checked pages. If yours does not match, use the search box in the Settings app and type 'Wi-Fi Calling' or 'VoLTE'.

1. 1iPhone: WiFi CallingApple gives the path Settings > Cellular (or Mobile Data) > Wi-Fi Calling, then turn on the switch for the line you want; with several SIMs, pick the line first. Some Thai carrier guides say Settings > Phone, depending on the iOS version they were written for. We found no Apple page confirming an iOS 26-specific path, so use the Settings search if you cannot find it.
2. 2iPhone: VoLTEGo to Settings > Cellular > Cellular Data Options. If your carrier supports VoLTE, Apple says you will see Off, Voice & Data and Data Only. Choose Voice & Data to call over LTE; with Data Only, calls do not run over LTE. On newer iPhones some carriers show a Voice & Data menu with a VoLTE switch inside it.
3. 3Samsung Galaxy (One UI): VoLTE and WiFi CallingVoLTE: Settings > Connections > Mobile networks > VoLTE calls (some models say 4G Calling or LTE calls; on dual SIM, pick the SIM first). Some newer models have no switch because VoLTE is always on. WiFi Calling: open the Phone app > three-dot menu > Settings > Wi-Fi calling, or add the tile to Quick settings.
4. 4Other Android phones (Pixel, Xiaomi, OPPO)Most put them on the SIM page. Pixel: Settings > Network & internet > SIMs > choose the SIM, where you will find Wi-Fi calling and VoLTE (or 4G Calling). Xiaomi/HyperOS: Settings > SIM cards & mobile networks > choose the SIM. These menu names come from community and tech sites rather than manufacturer pages, and may differ by carrier and across Android 14 to 16.
5. 5Check which path a call is usingiPhone: open Control Center; 'Wi-Fi' after the carrier name means WiFi Calling. Android: a phone-with-Wi-Fi-waves icon appears in the status bar. For VoLTE, some models show a VoLTE or HD icon, and the network indicator stays at 4G/5G during the call; if it drops to 3G mid-call, VoLTE is not in use. On many Android phones, dialling *#*#4636#*#* opens a Phone info screen with an IMS Service Status menu showing whether VoLTE and VoWiFi are registered (this comes from community sources, and some models disable it).

How to turn on WiFi Calling on every brand, step by step

Which is better, WiFi Calling or VoLTE, and should you keep both on?

Neither wins everywhere; each is good at a different job. VoLTE is steadier where there is 4G signal, because the network reserves quality for voice, and it works anywhere your carrier has towers. WiFi Calling helps where towers do not reach, such as basements, rooms deep inside tall condos, and abroad. For most people the advice is to keep both on, since the phone picks whichever path works. With VoLTE off, calls must lean on 3G/2G, which sounds worse and no longer exists in some countries.

Start with the basics: what WiFi Calling is and how it works

See data-only travel eSIMs (no phone number)