With customers driving the demand for always on connectivity, mobile phone networks are turning to Wi-Fi to enable services that their own masts might not be able to provide.

That's a good thing for those who want to remain connected in an area that perhaps doesn't support a particular network, letting you take calls and get messages where the cellular network might not reach.

But what is Wi-Fi Calling, what does the service offer, who supports it and on what devices?

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Wi-Fi Calling is exactly what you're thinking: a feature that allows you to make and receive calls (and send text messages) over a Wi-Fi network instead of a traditional mobile network.

More specifically, with Wi-Fi Calling, cellular packets of a phone call or text message are transferred over the internet from your mobile device to your carrier (whilst utilising higher data speeds than most cellular connections), then piped through the cellular network, and finally delivered to the intended recipient. Simples, right?

It's a handy feature should you find yourself in an area with poor signal, because it lets you take advantage of Wi-Fi so your device is connected. That might be in rural areas with no network masts by using domestic Wi-Fi, or a basement nightclub that has Wi-Fi.

To use Wi-Fi Calling you need two things. You need a network that supports it (which we list below) and you need a device that supports it (also listed below).

However, there's a slight catch in that you probably need a device sold by the network you intend to use it on, so you have the right software on it to access the network service. 

In the case of EE - the first network in the UK to launch Wi-Fi Calling - you will have to have bought your Android phone directly from them to use Wi-Fi Calling. If you have an unlocked handset you've moved from another network, or you bought a grey import, there's a good chance you won't be able to use the service. The same is true of Vodafone. With iPhones, any unlocked compatible model should work. 

For many customers on a regular monthly payment plan, with a handset from their network, there should be no problem at all, as long as that handset supports Wi-Fi Calling.

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Several popular apps - including messenger apps like WhatsApp, Facebook Messenger and Skype - allow you to send and receive calls/texts over Wi-Fi or your data network, but this isn't Wi-Fi Calling.

When using an app like WhatsApp, your calling activity is kept strictly within the app itself and between users of that app. Your phone number is used to verify your identity, but it has nothing to do with the network at all, other than the data you use.

Similarly, Apple's FaceTime and iMessage hand off calling and messages to internet services using the device's data connection, but that's an Apple service, rather than from your network.

In some cases, like iMessage, you get unlimited messaging and it's seamlessly integrated for use between Apple device users, but it's distinctly different from the proposition around network Wi-Fi Calling, where messages you send and calls you make will (probably) be deducted from your talk plan.

If you're an O2 or Three customer, this might all sound familiar. O2 has had a service called TU Go for a while now, and Three has a service called InTouch which has now been replaced by full embedded Wi-Fi Calling on some devices.

These will allow you to make calls over Wi-Fi, but you have to be using the apps for it to work. It's a separate solution and the beauty of Wi-Fi Calling is that it's seamless and integrated, without the need for an additional app on your phone.

The idea is that it's a lot simpler, because with network-enabled Wi-Fi Calling, you literally don't have to do anything at all, it just works.

The major downside to Wi-Fi Calling is that ongoing phone calls cannot always transfer back to your mobile network when kicked off Wi-Fi, yet.

So, if you start a call on Wi-Fi while at Starbucks, but then wander out of range, your mobile network won't be able to pick up the call. That is until the networks provision VoLTE (voice over LTE). 

Currently, when you place a voice call, your device switches to 2G or 3G and you cannot move a call to or from Wi-Fi. However, if or when your network supports VoLTE (also called 4G Voice) then you'll be able to move that voice call from Wi-Fi back to the network without dropping your call.

In the UK, both EE and Three have rolled out VoLTE, the latter did so through a service with the snappy brand name "4G SuperVoice" which uses the lower frequency networks it rolled out in some rural areas. But despite promising a launch way back in 2015, neither Vodafone or O2 have yet pushed out their versions. 

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Here's a list of networks that currently enable Wi-Fi Calling in the UK and US:

  • EE enabled Wi-Fi Calling on its network in April 2015
  • Vodafone switched on its Wi-Fi Calling service in September 2015
  • Three powered up its app-free Wi-Fi calling service in January 2017

O2 hasn't enabled Wi-Fi Calling yet, but it does currently offer an app called TU Go with similar functionality, as mentioned above. While Three has enabled Wi-Fi on some devices, others without the baked-in feature can make use of the service by downloading the InTouch app as before. 

  • T-Mobile enabled Wi-Fi Calling when Apple introduced the feature with iOS 8
  • Sprint enabled Wi-Fi Calling on its network after Apple expanded support with the iOS 8.3 update
  • AT&T launched Wi-Fi Calling for iPhone customers in late 2015, with some Android devices following suit in June 2016. 
  • Verizon launched Wi-Fi Calling on select Android phones in late 2015, with iPhone's being added in March 2016

While T-Mobile and Sprint have had Wi-Fi calling available for some time, the big two network providers in the States didn't launch their services until relatively recently. 

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Here's a list of devices that currently available that support Wi-Fi Calling, with links to their websites for more information about the devices as well as how to turn on the feature:

  • EE UK (website) - iPhone 7, iPhone 7 Plus, iPhone SE, iPhone 5S, iPhone 5C, iPhone 6, iPhone 6 Plus, Google Pixel, Google Pixel XL, Samsung Galaxy S7/S7 Edge, Samsung Galaxy A5 (2017 and 2016), Samsung Galaxy A3 (2017 and 2016), Samsung Galaxy S6/S6 Edge, Sony Xperia X, Sony Xperia XZ, Sony Xperia XA, Sony Xperia X Compact, BlackBerry PRIV, LG K8 LTE, LG G5, HTC 10
  • Vodafone UK (website) - iPhone 7, iPhone 7 Plus, iPhone 6s, iPhone 6s Plus, iPhone SE, Samsung Galaxy A5 (2017 and 2016), Samsung Galaxy A3 (2017 and 2016), Galaxy S6/S6 Edge, Galaxy S7/S7 Edge. 
  • Three UK (website)- iPhone 7/7 Plus, iPhone 6s/6s Plus, iPhone 6/6 Plus, iPhone SE, iPhone 5s, iPhone 5, iPhone 5c, Samsung Galaxy S6/S6 Edge, LG G5. (Galaxy S7/S7 Edge coming soon). 
  • T-Mobile USA (website) promised to enable Wi-Fi Calling for all its devices
  • Sprint USA (website) - iPhone 5C, iPhone 5S, iPhone SE, iPhone 6/6 Plus, iPhone 6s/6s Plus, iPhone 7/7 Plus. 
  • AT&T USA (website) - iPhone 7/7 Plus, iPhone 6s/6s Plus, iPhone SE, Samsung Galaxy S7/S7 Edge/S7 Active, Galaxy S6 Edge, LG K10, LG V20, LG V10, LG G5.
  • Verizon USA (website) - iPhone 6s/6s Plus, iPhone SE, Samsung Galaxy S7/S7 Edge, Galaxy S6/S6 Edge, Galaxy J3 V, HTC 10, BlackBerry PRIV, LG V20, LG G5, LG Stylo 2 V, Moto DROID Turbo 2. 

Naturally, this list will change over time, so you can expect wider support than just those devices we've mentioned. 

One of the important things to note about Wi-Fi Calling is that it needs carrier/network software to enable it. In the case of EE and Vodafone in the UK, you have to have bought your device from the carrier for it to work with Wi-Fi Caling. If you buy your device elsewhere, it lacks the network-specific software it needs for the service to function, as we talk about above.

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Your phone should come with an instruction manual that explains how to set up Wi-Fi Calling, but you could just go to your carrier's website (links above) to find step-by-step guides. Most of the time you'll need to switch on an option under Settings, and perhaps notify your carrier that you plan to use Wi-Fi Calling.

Once you're set up, simply use your phone as normal. You should see a new symbol (see top image) at the top of your phone when using Wi-Fi Calling. Keep in mind the other person/recipient doesn't need a device that supports Wi-Fi Calling (nor does he or she need to enable it with a carrier) for the feature to work.