This article titled “What is Wi-Fi calling and will it solve my mobile phone black spot?” was written by Samuel Gibbs, for theguardian.com on Tuesday 7th April 2015 05.00 UTC

Mobile phone signal not quite as reliable as it should be? Getting a signal strong enough to make a call outdoors normally isn’t a problem, but indoors can be a completely different matter?

Wi-Fi calling aims to solve indoor mobile black spots by allowing users to send and receive phone calls and text messages without using the mobile phone network.

What does it do?

Wi-Fi calling, as the name suggests, routes voice calls and text messages over the internet using a Wi-Fi network, connecting to the mobile phone operator without having to be connected to the network itself.

Is that not just Skype?

Several apps and services allow users to place calls over the internet (VoIP), and while it has the same effect, Wi-Fi calling is a whole different animal. Skype, for instance, uses a separate number and service and cannot be used for calls to emergency services for instance. Apple’s FaceTime only works between compatible Apple devices and cannot call landlines or other brands of smartphone.

Wi-Fi calling replicates all the features and characteristics, including HD calling for smartphones that support it, of a standard mobile phone call using the same number and without relying on the mobile phone network or a separate app.

Why should I care?

Wi-Fi calling means that users can place calls in mobile phone black spots, as long as they have access to an internet connection.

How does it work?

The smartphone connects to the mobile phone operator via the internet rather than the mobile phone network, which sounds incredibly simple but allowing that sort of connection requires a new set of technologies.

EE, for instance, uses a system called IP Multimedia Subsystem (IMS), which essentially allows insecure connections from outside the company’s network acting as an interface between the internet and the mobile phone network, which then carries the call or text message on to the recipient.

What do I need to do?

The beauty of Wi-Fi calling is its simplicity. It requires no app, no additional number or service and doesn’t cost anything over and above your existing mobile phone contract. Users simply need to check a box on a compatible smartphone and connect to Wi-Fi. That’s it.

Where can I use it?

Anywhere with a Wi-Fi connection that you can use to get internet access, but primarily work or home Wi-Fi.

How much broadband will I need?

Voice calls and text messages don’t take up much bandwidth, so a connection in excess of 0.5Mbits per second, should be able to support Wi-FI calling.

What if I leave home or the office?

When taking a call on Wi-Fi the call is limited to that network. If the Wi-Fi drops out, when the user leaves home and the range of the network for instance, the call will drop too. There is no seamless handover between Wi-Fi and the mobile phone network for voice calls.

When can I get it?

EE’s Wi-Fi calling launches today. Other UK mobile phone operators are likely to follow in the near future.

On which devices does it work?

Not all smartphones support Wi-Fi calling. EE’s service is available on Apple’s iPhone 6, 6 Plus, 5S and 5C with a software update and will launch on Samsung’s new Galaxy S6 and S6 Edge, as well as Microsoft’s Lumia 640 from 10 April. Several other devices, including the Samsung Galaxy S5, will come at a later date.

What are the alternatives?

Other British mobile phone operators offer similar services using apps, which have advantages and disadvantages compared to Wi-Fi calling but are not baked into the smartphone phone dialler and services.

Three’s inTouch app for Android and iPhone allows Three customers to place calls and send text messages through the app when connected to Wi-Fi but not the mobile phone network. Like EE’s Wi-Fi calling, the inTouch app only works within the UK, but will work when connected to portable hotspots for other mobile networks.

O2’s TU Go app is slightly more advanced. Available for the iPhone, iPad, Android, Windows Phone and Windows, TU Go allows O2 customers to place calls, send texts and check voicemail over the internet, but will work on non-smartphones including computers and tablets, which wouldn’t ordinarily be able to make or receive calls or messages.

TU Go can also be used abroad, and can call multiple devices at the same time.

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