What you need to know about Wi-Fi calling

Curious about Wi-Fi calling and what it entails? CNET has the rundown on what you need to know.

A Wi-Fi network can place calls when you're trapped in an area with spotty phone signal. James Martin/CNET

Editors' Note:This article has been updated on October 8, 2015 to incorporate AT&T's Wi-Fi calling capabilities.

In addition to offering customers a cheaper alternative to their phone plans, one of the main draws of Google's newly launched Project Fi service is that it will seamlessly switch a user's phone service from cellular to Wi-Fi.

Wi-Fi calling is nothing new; apps like Skype, Google Hangouts and WhatsApp make it easier for smartphone users to place calls over the Internet and forgo mobile networks altogether. But as this option becomes increasingly more beneficial to users, carriers have shown increasing interest in adopting Wi-Fi calling themselves. Whether it's because they want to bolster their network coverage or improve user experience, some US carriers already provide the service, and now Google has jumped into the ring as well.

To help you make sense of what Wi-Fi calling is, why it's important, and what you can use it for, CNET put together a handy guide to walk you through everything you need to know.

Editors' Note:This piece has been updated on April 22, 2015 with clarification from T-Mobile and information about Google's Project Fi initiative.

What is Wi-Fi calling?

Instead of using your carrier's network connection, users can make voice calls through a Wi-Fi network. That can include a Wi-Fi connection you have set up at home, or whatever Wi-Fi hotspot you happen to be on when you're out and about, such as a cafe or library. In most ways, it's like any other normal call, and you still use regular phone numbers.

Why would I want that?

Wi-Fi calling is especially useful when you're in an area with weak carrier coverage. For example, when you're traveling to the residential countryside, or you're in a building with spotty reception. You may already be familiar with using Wi-Fi to send messages when SMS texting is unavailable (apps like Kik and Facebook Messenger provide these services) -- and the same applies for when you're trying to place a call. With Wi-Fi, you can call a friend up even if you're in a dingy, underground bar (assuming you can connect to the bar's Wi-Fi, that is.)

Isn't that what Skype does?

Built-in Wi-Fi calling has some advantages over third-party services like Skype. Nicole Cozma/CNET

In a way, yes. There are various services including Skype, Viber, WhatsApp and Facebook Messenger that provide what's known under the umbrella term as "voice over Internet Protocol" to make calls with either a Wi-Fi or data connection.

Carrier-branded Wi-Fi calling is a bit different, however. It's baked directly into the phone's dialer, so you don't need to fire up an app or connect to a service to use it. You can set it as your default way of placing a call, or if you lose phone signal, it will automatically switch to Wi-Fi calling.

Because the service is built-in, that also means you don't need to add contacts to a service as you do with Skype. You'll have access to your existing phone book, and your friends can receive your Wi-Fi call without needing to download a third-party app. With no contacts to add, carrier Wi-Fi calling requires little effort to set up.

What carriers and phones support this service?

Of the four major US carriers, T-Mobile, Sprint, and AT&T provide built-in Wi-Fi calling. Though no official timeline has been set, Verizon has confirmed plans to offer the service. In addition, Republic Wireless provides Wi-Fi calling by default on its handsets, and users get support from Sprint's network if connection is unavailable.

Currently, T-Mobile has 23 smartphones that support this option, including the Apple iPhone 6S and 6S Plus ; Samsung Galaxy Note 5 and S6 Edge Plus ; the LG G4 and HTC One M9 .

As for Sprint, Wi-Fi calling is available on the iPhone 6 Plus, 6, 5S and 5C only if its iOS software is updated to v8.3. A number of Android devices have the service as well, but to see if yours has it, you'll need to check through the handset's Settings menu.

Currently, AT&T offers Wi-Fi calling only for the latest Apple iPhone 6S and 6S Plus , as well as the previous iPhone 6 and 6 Plus .

Of the four major carriers, only T-Mobile and Sprint support the service. Josh Miller/CNET

Does it cost more?

It doesn't cost any extra as such, but making calls over Wi-Fi can come out of your regular minutes allowance depending on your carrier, your phone plan and which country you're calling to/from. Under T-Mobile's specific "Simple Choice Plan," for example, Wi-Fi calling does not impact minutes. But be sure to check with T-Mobile and Sprint's policies to see if any of their potential restrictions and charges relate to your situation.

If you're running out of minutes, then using services like Skype or WhatsApp will help you avoid incurring any additional charges.

Can I use it overseas without paying huge amounts?

Again, that depends. T-Mobile lets you make and receive Wi-Fi calls for free between 120 countries. Sprint customers won't be charged for calls made to, from, or between the US, the US Virgin Islands and Puerto Rico, but they will be charged "international calling plan rates" for other countries. Republic Wireless only supports Wi-Fi calling for the US and Canada. Other than that, the carrier has no international support, which includes no support for Puerto Rico, Guam and the US Virgin Islands.

If you're going abroad and want to keep in touch, its best to stick with Skype and WhatsApp when you're connected to a building or hotel's Wi-Fi. You can use data, but remember that it will cost you a lot if you're roaming on cellular networks. If you don't have a roaming plan, make sure you only use Wi-Fi and turn off data roaming in your Settings before heading out.

Do I need a fast Wi-Fi connection?

Though the higher throughput you have the better your connection will be, a minimum of 1Mbps should be enough to patch a solid call through. Republic Wireless reports that it can hold a call with 80kbps, but the quality may decrease and you'll experience more dropped calls as well.

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