Entitlement Servers, VoWi-Fi, and the new era of Voice

The rise and fall and rise of Voice

There was a time, in the first few years after the millennium, when it looked like voice calling was going to die off entirely. WhatsApp launched in 2009, offering ‘free’ messaging using your data connection, bypassing relatively expensive SMS charges. Why would anyone pay to make a voice call when they could send a quick free text?

There were ways to make a call over a data connection. The first commercial VoIP service was VocalTec InternetPhone, which launched in February 1995, and by 2003 Skype successfully brought internet calling to the home PC market. It looked like the medium would go the way of physical mail or fax: used only for formal occasions, doctors’ appointments and elderly relatives.

It wasn’t until 2013 that WhatsApp initially offered voice via data, and that didn’t achieve anything like real-time calling until 2014. This was a long dark time for Voice, but it survived its traditional circuit-switched past to thrive again as an IP-based service.

This return was driven by later-gen Over-the-Top (OTT) voice applications like WhatsApp and Signal, which challenged Mobile Network Operators (MNOs) and their pay-per-minute voice revenue streams.

But there’s been an unexpected third act for Voice, as the MNOs reclaimed customers by adopting innovative Voice-over-WiFi (VoWi-Fi) services.  

What is VoWi-Fi?

VoWi-Fi integrates Wi-Fi access with the MNO's core IP Multimedia Subsystem (IMS), which allows for clear, lag-free and carrier-grade voice calls over Wi-Fi using a device’s native dialer and existing phone number.

It quickly became a strategic tool for MNOs, improving indoor coverage, offloading voice traffic from congested Radio Access Networks (RAN), enhancing voice quality, and competing with the OTT services. The VoWi-Fi market has seen vigorous expansion, highlighting that the market isn’t done with Voice yet.  

The deployment of VoWi-Fi and related services like Voice over LTE (VoLTE) depends on a critical and ‘hidden’ network component called the Entitlement Server (ES). These servers act as gatekeepers, managing subscriber and device authorization for specific network features. The ES is fundamental to VoWiFi activation and management.  

Entitlement Servers manage a wide array of network features, including eSIM provisioning for primary and secondary devices like Wearables, 5G service access, and mobile hotspot tethering. This centralized and rapidly automated control is vital as mobile services diversify and accelerate.

The gatekeepers of mobile service

1GLOBAL has written previously about the essential role of the ES in modern telco ecosystems but, as a quick refresher, the ES basically allows mobile operators to manage the services accessible to end-user devices. They ensure that only authentic subscribers use specific services, and provide the device configuration to make it happen.

The ES automates the complex process of making sure connection and devices comply with industry standards crucial for interoperability, like GSMA's TS.43 Service Entitlement Configuration. For ES platforms to work with both Apple and Android devices, they must meet specific requirements for enabling services like VoWi-Fi on Apple specs as well as GSMA TS.43.  

How does ES activate VoWi-Fi?

VoWi-Fi activation involves complex coordination between the device, the ES, and several core network elements.

First, a VoWiFi-capable device queries its eligibility for VoWi-Fi service upon detecting a Wi-Fi connection.

Second, the device securely communicates with the MNO's ES. The ES, often with the 3GPP Authentication, Authorization, and Accounting (AAA) server and Home Subscriber Server (HSS) / User Data Management (UDM), authenticates the device and subscriber, typically using Extensible Authentication Protocol - Authentication and Key Agreement (EAP-AKA) with SIM or eSIM credentials.

Third, the ES verifies the subscriber's profile and service permissions with MNO backend systems (BSS/OSS) to confirm if the user’s plan includes VoWi-Fi and the device is authorized.

Finally, if so ‘entitled’, the ES dynamically activates VoWi-Fi and pushes a config via protocols like Evolved Packet Data Gateway (ePDG) to the device. This may also include managing emergency address registration and presenting terms and conditions via websheets.  

This entire process has to be done as close to instantly so as the customer can’t tell the difference, across hugely varying OS, device generations and network conditions.  

VoWi-Fi saved the radio tower

As a benefit to the operator, VoWi-Fi functionality offloads voice traffic from the MNO's own licensed and potentially metered Radio Access Network (RAN) cellular towers on to local networks. Voice packets travel over the user’s own Wi-Fi, then the internet to the ePDG, and into the MNO's core network. This frees RAN capacity, reducing costs and improving indoor coverage where cellular signals are weak but Wi-Fi is robust.

The carrier native advantage

VoWiFi offers a ‘carrier-native’ experience, meaning it uses the device’s standard dialer, contacts, and call history without needing a separate app. It also utilizes the user's existing phone number and can achieve uninterrupted handoff between Wi-Fi and cellular as the user moves in and out of coverage. The user’s device will manage the handoff based on Wi-Fi quality (RSSI, packet loss) and cellular conditions as defined by the carrier config and the device OS.   

This deep network integration backed up by eSIM-based security is a big differentiator between VoWi-Fi from OTT services. Like many of the services and functionalities that ES enables, the strength of the offering comes from drastically reducing the interactions and ‘clicks’ required of the user.

Calling plans and revenue

VoWi-Fi has played a huge role in reshaping the mobile telco market in terms of pricing and operator revenue models, and is making the idea of ‘calling minutes’ as redundant as free SMS allowances. 

While some operators still count VoWi-Fi calls against minute allowances, customer behavior is strongly favoring pure data models, as voice revenue stagnates and data volume is increasingly central to the average revenue per user (ARPU).  VoWi-Fi has enabled the prevalence of plans with (functionally) unlimited Voice, where pricing is based on bandwidth and volume.

In both postpaid and prepaid segments, VoWi-Fi is a huge step up in terms of coverage and call quality. While it’s a fairly unusual example of tech providing fewer revenue streams, as direct voice income falls, it has also significantly improved service and boosted customer satisfaction, reduced churn, and positively impacted long-term ARPU.   

VoWi-Fi market growth

While VoWi-Fi use is less immediately profitable to monetize minute by minute, it’s also a huge growth market. Analyst projections show significant growth, with recent reports estimating a rise from €7.8 billion in 2023 to €28.8 billion by 2032, representing a robust 15% CAGR.

While key drivers for the expansion certainly include improved quality and reliability, the overwhelming motivator is cost. While North America is still the largest market, likely due to the prevalence of advanced devices, the APAC region is significantly faster growing due to being more price motivated.  

Analysts have identified VoWi-Fi's offloading of voice on to customer’s own broadband as having significantly reduced the cost of MNO market entry and operation, enabling a lot of new competition, and further cementing ‘unlimited voice’ as a standard feature in plans.  

VoWi-Fi vs. OTT

Naturally, it’s in the interest of OTT platforms like WhatsApp and Signal to encourage users to make the extra few clicks to open their apps, rather than fall back on the convenience of a native dialer. OTT services not only require a separate app, but both parties typically need that same app, which makes VoWi-Fi's ‘zero-barrier’ approach a key convenience.  

There’s an ongoing feature race between the OTTs and MNOs, although in practice the work of the latter is being done by tech specialists such as 1GLOBAL, who provide and innovate the ES architecture.

In terms of quality, VoWi-Fi can offer HD voice (AMR-WB) via the MNO's IMS core, with potential for QoS management (e.g., IEEE 802.11e/WMM). However, end-to-end QoS can be challenging over unmanaged Wi-Fi, and OTT apps have had success in developing adaptive codecs including WhatsApp’s MLow and Signal's Opus to stabilize performance over shaky internet.

Security is increasingly an issue and has recently brought secure messaging apps a lot of unwanted international attention due to breaches in encryption.

VoWi-Fi uses SIM-based authentication (EAP-AKA) and IPsec tunnels (IKEv2/ESP) for security and is typically not end-to-end encrypted (E2EE), which in practice has helped boost its popularity as law enforcement jurisdictions are less wary of licensing tech they can lawfully intercept.

In contrast, apps like Signal and WhatsApp champion E2EE using systems like the Signal Protocol where (in theory) only sender and recipient can decrypt content.

Looking to the future, it seems like the MNOs and VoWi-Fi are likely to gain the upper hand as 5G has a growing impact. Both the GSMA and 3GPP are working on convergence with 5G core networks (5GC), leveraging the opportunity for enhanced 5G security and authentication. VoWi-Fi also promises to take advantage of satellite backhaul connectivity, which enables voice calls even in maritime and in-flight scenarios.

The redefined future of Voice  

Entitlement Server solutions, developed by tech pioneers like 1GLOBAL, have been pivotal for the modern mobile service landscape, enabling VoWi-Fi among many other advanced features. They’ve transforms voice delivery, moving the market away from per-minute billing to a pure data model, where unlimited voice is standard.  

Agile MNOs must invest in robust IP infrastructure and prioritize quality of experience to use VoWi-Fi for cost efficiency and service differentiation.

Entitlement Servers remain the largely unseen and unsung heroes of the telco market, ensuring Voice as a medium finds its new role as a versatile, integrated, and ubiquitously accessible option. The focus continues to shift from counting minutes to guaranteeing high-quality, reliable connectivity, with ES orchestrated VoWi-Fi at the core of this redefinition.

To learn more about how your business can seamlessly enable new products or network features such as VoWiFi on your subscribers’ devices, visit:
Entitlement Server for Apple, Android Devices & Network Features