Technology that makes it possible to make calls even without mobile phone signals

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A man in a dark gray long-sleeved shirt sits at a wooden table in a dim, concrete-walled room, staring intently at a black smartphone displaying "NO SERVICE" in red. A silver laptop on his right shows a smiling person on a video call, and the two screens contrast sharply. A single bare bulb lights the scene, while an open doorway behind him reveals a dark concrete stairwell. A blurred stack of papers and folders sits on the left of the table, and his serious expression suggests worry.
Staring down "NO SERVICE" while a cheerful video call carries on beside him.


 Technology and Mobile Signal

 

Imagine you are in the basement of a building. Light fills the room, the air conditioner keeps the outside heat at bay, your laptop is connected to Wi-Fi, and the internet speed is decent.

 

While you work peacefully, you suddenly remember you need to make a very important phone call. You immediately pull your mobile phone from your pocket, but your heart sinks the moment you glance at the screen.

 

The mobile network is gone. There isn't a single signal bar.

 

The problem is that the person you need to contact can’t access to WhatsApp, Zoom, or any other internet-based calling service—in fact, they don't even use a smartphone.

Even with internet access, you can’t make a standard phone call.

Before reading this, you probably assumed that the only way to get a signal in a basement was to step outside or move to higher ground.

 

But what if you knew that, in certain situations, you could still make phone calls using your existing mobile number—even when there is no mobile signal?

 

This is made possible through a feature known as Wi-Fi Calling, which the Pakistan Telecommunication Authority (PTA) recently highlighted in a public awareness campaign.

 

With this feature, users can make voice calls or send SMS messages over a Wi-Fi network, even when they have no signal from their mobile network operator.

 

In a message released on social media platforms to raise public awareness, the PTA (Pakistan Telecommunication Authority) states: "You may face difficulty making calls while indoors, in a basement, or in any other location where mobile signals are weak. In such situations, Wi-Fi calling—also known as VoWiFi—can be helpful."

 

The question arises: how exactly does a call go through when there is no connection to a mobile tower? How does this differ from calls made via WhatsApp or other internet-based services? And how can a mobile phone user take advantage of this feature?

 

How does Wi-Fi Call Work?

 

Wi-Fi is an essential part of everyday life, so it needs no introduction. It allows mobile phones, computers, and other devices to connect to the internet within a specific area.

 

Meanwhile, "VoWi-Fi" (Voice over Wi-Fi) is known as Wi-Fi calling.

 

According to the GSMA—the international organization representing mobile network operators worldwide—VoWi-Fi refers to the seamless delivery of voice services directly over a Wi-Fi network.

 

A woman in a dark long-sleeved shirt and a large green backpack stands on a rocky outcrop, holding a walkie-talkie to her ear with a worried expression, her dark hair pulled back. In the foreground, a smartphone lies face down on the rock, as though set aside or out of reach. Behind her, forested mountains stretch into the distance under a clear sky, lit by early morning or late afternoon light.
Radio in hand, phone abandoned on the rock, she listens for an answer in the mountains.

In Wi-Fi calling, your phone relies on a home or office Wi-Fi network instead of a mobile tower.

But if there is no signal available, how does the call reach the mobile network?


This question was posed to an expert in Information and Communication Technology (ICT).

 

To answer, the expert first explained how a traditional mobile phone call—one made using a mobile SIM and a mobile network—reaches its destination.


The expert explains that during a traditional phone call, your mobile phone first connects to the nearest mobile tower. This tower relays your call to the mobile operator's network. The network then routes the call to the tower located near the recipient, from where it is finally delivered to their mobile phone.

 

In other words, if you are in Lahore and calling someone in Karachi, your voice does not travel directly to their phone. It reaches the recipient by passing first through the tower nearest to you, then through the mobile company’s network, and finally through the tower nearest to the recipient.

 

Wi-Fi Calling

 

The process works somewhat differently with Wi-Fi calling.

According to an expert, when a mobile phone uses Wi-Fi calling, the initial leg of the call’s journey takes place through a Wi-Fi network rather than a mobile tower. In other words, the call first travels via Wi-Fi and the internet to reach the mobile operator's system; from there, the remainder of its journey follows much the same path as a conventional, traditional phone call.

An expert explains that when you initiate a Wi-Fi call, your voice is converted into internet data—similar to sending photos, videos, or WhatsApp messages over the internet. This data then travels via a secure path—through Wi-Fi and the internet—to your mobile operator's network. At that point, the operator verifies that the call is indeed originating from your mobile number.

Experts further note that the mobile operator then routes the call to the intended recipient, just as it would a standard phone call. If the person on the other end is using a mobile phone, the call reaches via a nearby mobile tower; if they are using a landline, the call uses the relevant telephone network.

 

According to an expert, "To the user, this entire process feels no different—the same mobile number is used, and the person on the other end is not even aware that the call was made via Wi-Fi rather than through a mobile tower."


A man in a dark long-sleeved shirt and dark pants sits at a wooden desk, eyes fixed on a laptop screen showing a video call with another man, his left hand on the keyboard while his right hand holds a black smartphone he's also checking. Papers and a coffee cup sit on the desk in front of him. Behind him, a concrete wall carries a sign reading "BASEMENT B-2" along with exposed wires and a white wall-mounted box. In the dim background, another person is faintly visible at a desk lit by a lamp.
Working a video call and a phone at once in the basement workspace.

How Users Utilize Wi-Fi Calling, and How Does It Differ from a WhatsApp Call?

 

If Wi-Fi calling also relies on the internet, how does it differ from calls made via platforms like WhatsApp, Signal, or Telegram? According to an expert, the main difference between the two is that Wi-Fi calling is part of a mobile operator’s voice service, whereas calls made via WhatsApp or similar apps take place on the respective company’s internet platforms.


An expert added that when using Wi-Fi calling, you use the same mobile number linked to your SIM card. The person receiving the call does not need to have a specific app, an internet connection, or a smartphone.

 

"For example, if you wish to reach a landline number, it is possible via Wi-Fi calling; in contrast, WhatsApp calls can only take place between users who are both using WhatsApp."

 

Pakistani Mobile phone operators are offering a Wi-Fi calling facility, and guidelines are available on their respective websites.

 

According to the details available on these websites, not every user can avail of this facility; certain technical requirements must be met.

 

Mobile operators state that to use Wi-Fi calling, a user must have a mobile phone that supports VoWiFi and VoLTE. Additionally, the phone must use a 4G/LTE SIM, and the user must have a balance or an active voice call and SMS package.

 

The mobile operator Jazz states that this feature has been tested on various phone models such as Samsung, Oppo, Vivo, and Digit. Meanwhile, another operator, Zong, notes that most modern smartphones—including those from Samsung, Apple, Huawei, Xiaomi, and others—support VoWiFi.

 

This raises a question: what exactly do "LTE" and "VoLTE" mean?

 

LTE stands for "Long-Term Evolution." In simple terms, LTE is the technology commonly referred to as 4G. When a "4G" or "LTE" icon appears on your phone, it indicates your device is utilizing high-speed mobile internet.

 

On the other hand, VoLTE stands for "Voice over LTE." With this technology, phone calls are also conducted via the 4G network. In the past, mobile networks would switch from 4G to 3G or 2G during a call; however, with VoLTE, the call remains on the 4G network, which can result in better voice quality.


A woman with short brown hair, a gray fleece jacket, and a dark green backpack stands on a rocky outcrop, looking down at the walkie-talkie in her right hand — a dark gray unit with a small green screen. Beyond her, a broad mountain valley opens up, layered blue and green peaks fading toward a pale, clear sky, with dark forest filling the valley floor and lower slopes. The light suggests early morning or late afternoon.
Reading the walkie-talkie's display on a ridge above a wide mountain valley.

How can Wi-Fi calling be enabled, and what does it cost?

 

According to the mobile phone operators, if the user's phone has a Wi-Fi calling facility, it has to be enabled in the settings.

 

Android phone users can enable Wi-Fi Calling in their phone settings under Connections or SIM settings. However, there may be slight differences on the phones of different companies.

 

On the other hand, iPhone users can go to Settings, tap on the Cellular or Mobile Data option, and enable Wi-Fi Calling there.

 

Once this feature is enabled, the phone can use the call and SMS facility over the available Wi-Fi network in case of weak or non-existent mobile signals.

 

Pakistan Telecommunication Authority (PTA) says that users should contact their mobile operator if this option is not available in the phone settings or if there is a problem using the facility.

 

But does this convenience of calling via Wi-Fi instead of a mobile tower make users pay extra?


According to mobile phone operators, no additional fees are charged for Wi-Fi calling, but the same rates apply as for traditional calls or SMS.

 

This means that the facility for users is a continuation of a traditional mobile service, the only difference being that Wi-Fi calling uses a Wi-Fi network instead of a mobile tower.


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