What Is Wi-Fi Calling and How VoWiFi Works
No separate app or third-party account is needed to make a call. The subscriber keeps using their regular number, and the call is routed through the operator’s network.
After connecting to Wi-Fi, the smartphone establishes a secure connection (IPsec tunnel) between the device and a dedicated operator node — the ePDG (Evolved Packet Data Gateway). This node accepts the secure connection from the device and forwards the voice traffic into the network’s packet core.
On the network side, the IMS infrastructure then handles the establishment, routing, and termination of the voice call, so for the subscriber, VoWiFi looks almost identical to a regular mobile call.
How Wi-Fi Calling Differs From Regular VoIP
Both technologies carry voice over an IP network, but they differ in how the service is delivered and the infrastructure the call passes through.
VoIP is a general method of transmitting voice data over IP. It is used, for example, by internet telephony, corporate communication systems, and calling apps.
VoWiFi is a carrier service integrated with the mobile network. The call is processed by the operator’s infrastructure and is tied to the subscriber’s number and communication services.
| Characteristic | VoWiFi | Regular VoIP |
| Phone number | Uses the regular mobile number | Depends on the service |
| SIM card | Used to identify the subscriber | Usually not required |
| IMS | Used in the operator’s network architecture | Not required |
| Separate app | Usually not required | Often required |
| Network | Wi-Fi with access to the operator’s network | Any IP network with access to the VoIP service |
When Wi-Fi Calling Is Used
VoWiFi is used where the mobile signal is insufficient for stable voice communication but Wi-Fi access is available.
The technology is especially useful inside buildings with poor radio signal penetration, in underground spaces, and other areas with weak coverage. Wi-Fi Calling can also be used in situations where the operator provides access to the service over Wi-Fi while roaming.
Find out how a Sub-Saharan African operator launched Wi-Fi Calling to provide voice communication in conditions of insufficient coverage and an unstable mobile network signal — VoWiFi for an African LTE-Only MVNO: ePDG Deployment.
For the subscriber, VoWiFi makes it possible to keep using the familiar way of making calls even with a weak mobile signal. The cost of the call is determined by the operator’s terms, and the Wi-Fi connection itself may be provided separately.
Wi-Fi Calling vs. a Regular Mobile Call
In a regular mobile call, the device uses the operator’s radio network to transmit voice traffic. With VoWiFi, access to the operator’s network is provided over Wi-Fi.
| Characteristic | Regular Mobile Call | Wi-Fi Calling |
| Network access | The mobile operator’s cellular network (2G/3G/4G) | Any available Wi-Fi network |
| Works without cellular service | No | Yes, if Wi-Fi is available |
| Mobile number | Used | Used |
| Connection to the operator’s network | Directly, via the radio access network | Secured via the ePDG, provided by the same operator |
| Wi-Fi | Not required | Required |
Wi-Fi Calling for Mobile Operators
For operators, the Wi-Fi Calling service extends coverage in areas with weak or absent cellular signal — indoors, in basements, or in remote areas — without the need to deploy additional radio infrastructure. This requires network-side support, primarily an ePDG to secure and authenticate the Wi-Fi connection, as well as integration with the operator’s core network (EPC/IMS).
Stingray offers a solution for deploying VoLTE and VoWiFi services for mobile operators.
Stingray’s ePDG provides the functions needed to organize voice services over LTE and Wi-Fi and integrates with the operator’s existing infrastructure.
Frequently Asked Questions About Wi-Fi Calling
What is VoWiFi in simple terms?
VoWiFi is a technology that allows calls from a regular mobile number over Wi-Fi instead of the operator’s radio network. The service works as part of the mobile network, so the subscriber doesn’t need to use a separate app.
Do I need a separate messaging app for Wi-Fi Calling?
No. If the operator and the smartphone support VoWiFi, calls are made through the standard phone app.
Is Wi-Fi Calling secure?
When connecting over an untrusted Wi-Fi network, the device establishes a secure IPsec tunnel with the ePDG. This keeps the traffic between the device and the operator’s network protected, even when using a public or other untrusted access point.
Why is ePDG needed for VoWiFi?
The ePDG is used to connect the device to the operator’s packet core over an untrusted network. It establishes a secure connection with the device and forwards the traffic on into the operator’s network.
How does VoWiFi differ from calls over WhatsApp or Telegram?
VoWiFi is a mobile operator service that uses the subscriber’s number and the operator’s infrastructure. Calls made through messaging apps are ordinary internet services and operate independently of the operator’s voice infrastructure.
