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What is Wi-Fi Calling?

Wi-Fi Calling has been around for a long time. Voice calls have been transmitted over Wi-Fi either in the form of OTT applications such as Skype or as initiatives such as UMA and femtocells to enhance the reach of mobile voice services in subscribers’ homes.

The problem with OTT applications from an operator’s perspective is that the operator loses control. The UMA / femtocell initiatives have proven to be too expensive lacking widespread support among phone manufacturers. In an ideal world voice calling should be totally seamless for the user, built-in natively in the device and work over any network connection.

The technology has been available for some time but operators have been hesitant. They have wanted to protect their voice-related revenue including revenue from roaming charges. However, new business models allowing for flat-fee voice services, combined with the realization that users will use OTT applications for calls as much as they can, has removed the last obstacle for taking Wi-Fi Calling to the next level.

In September 2014, mobile operator T-Mobile pioneered this next-generation Wi-Fi Calling solution. This is a paradigm shift for Wi-Fi Calling as it is now implemented with native support embedded in the smartphones and working seamlessly through any Wi-Fi connection. Text messaging (SMS) also works in this way.


Wi-Fi Calling – What are the benefits?

The next-generation Wi-Fi Calling solution is just as seamless for the user as iMessage. Users will never have to consider whether or not they are connected to LTE or Wi-Fi. Voice calls and text will just work. From anywhere to anyone.

For mobile operators Wi-Fi Calling has become critical for customer retention, as subscribers in many countries are giving up their landlines. With the smartphone as the primary device for keeping in contact with friends and family, they will be forced to switch to a competing mobile operator if the mobile connection is poor or non-existing.


  • Single, uniform voice dialer on their smartphone.
  • Allows for voice services over any Wi-Fi network (home, office, hotspots).
  • Wi-Fi Calling provides better indoor coverage.
  • Seamless call transfer support between Wi-Fi and LTE (using VoLTE) and specific support in the device.
  • Roaming charges will be minimized, if the operator is using the same business model as T-Mobile.  A call from anywhere in the world will be charged as a mobile call in your home mobile network whenever you have access to the Internet over Wi-Fi.


  • Better indoor coverage compared to cellular macro base stations. This solves an increasing problem with the “radio tight” modern building structures.
  • Reduced churn.
  • With indoor coverage, subscribers can give up their landlines. By offering Wi-Fi Calling services now, mobile operators can expect higher customer acquisition rates.
  • Operators can get back in the driver’s seat making OTT players such as Skype and Viber less important to subscribers.
  • Wi-Fi is a low-cost solution to enhance voice service coverage.
  • Operators do not necessarily even have to invest in Wi-Fi footprint. They can instead rely on existing Wi-Fi networks.
  • Wi-Fi Calling is sharing similar infrastructure with IMS-based VoLTE.

Wi-Fi Calling – What are the potential drawbacks?

Wi-Fi Calling and QoS

It should be noted that by implementing a Wi-Fi Calling solution operators have to give up some control over QoS for voice, as the traffic will go over networks that they do not fully administer. However, through the ever-increasing capacity of Wi-Fi networks with 801.11ac providing Gigabit speeds and the improved capability to prioritize multimedia traffic with WMM, QoS will in most cases not be a major challenge. Also, Wi-Fi Calling is offering an alternative to cellular voice where the LTE network does not work at all or is of poor quality.

Wi-Fi Calling and emergency calls

As with any Internet-based voice service, emergency service operators can have a hard time tracking the user’s location. Upon registration of the Wi-Fi Calling service the user has to register a default location, usually the home address. The capabilities in Aptilo’s solution to map APs with location will improve location information in Wi-Fi networks over which the operator has control. Also, vendors such as Apple have collected data mapping location information using individual Wi-Fi access points. It remains to be seen how regulatory agencies will view this, but the location issue is not relegated to the Wi-Fi Calling solution only: the same kind of issue currently exists with OTT voice applications.