It's the reason you can chat to your friends in the US and your Granny on her landline, but you probably haven't given a moment's thought to what a VoIP app actually is - or what the heck VoIP even means. Read on for your quick guide on how to make voice calls over the Internet, and find out which apps you need to download ASAP.

You know the reason you’re able to talk to friends who are all around the world, organise group video chats and make calls to expensive landlines without getting a hefty phone bill all boils down to four letters? V-o-I-P.

We’re talking Voice over Internet Provider, and VoIP apps are what allow you to make calls through the Internet, as opposed to through your mobile phone provider’s network.

VoIP apps make it quick, convenient, and generally inexpensive for you to make calls. They work in different ways, whether you’re calling from PC to PC via an instant messenger service like Skype, or calling from an IP-enabled phone to a telephone network (like Vonage).

What’s more, VoIP apps aren’t just great for making calls: most include a messaging function, and many allow you to make video calls as well.

The big advantage of making VoIP calls is that they won’t eat into your phone minutes. This is especially a bonus if you’re making international calls to friends, family members, or business contacts.

Or if you’re trying to stalk your favourite celebrity in Hollywood (not that we’ve ever tried calling Ryan Gosling via his agent or anything).

Thanks to ever-faster Internet connection speeds, the quality of a VoIP call is now often the same as a call made through your mobile phone provider’s network.

VoIP is sounding even better than those Game of Thrones series 7 spoilers. What’s the catch?

VoIP is pretty fabulous – and has essentially revolutionised how we talk to people. Just remember, you do need Internet access to make a VoIP call. This also means that if you’re not making your calls through a WiFi connection, you will be tapping into your data allowance (unless you’re on one of Three’s All You Can Eat data plans).

As a general rule, expect to use up 0.5 MB of your allowance for each minute of VoIP conversation.

VoIP apps generally aren’t pre-installed on mobile phones, and most VoIP apps will require access to information such as your contacts and data, including your phone number, name, and email address. Some VoIP app providers will also ask you to set up a separate account with them.

To call anyone through a VoIP app they will need to have the same app installed – otherwise you won’t be able to talk to them through the app. On the plus side, most VoIP apps are user-friendly enough for even the least tech-adept people.

One thing to remember: don’t use VoIP apps to make emergency calls. 999 should always be your go-to for urgent situations.

Here’s a breakdown of some of the most popular VoIP apps and what you need to know about them…

Facebook Messenger
Since pretty much everyone on the planet has a Facebook account (there must be some research out there which confirms that even those who insist they’re “so over it” spend at least two hours a day scrolling through their exes’ profiles), which means this app is a no-brainer since it links right to your Facebook contact list.

Though separate from the actual Facebook app, it’s a great way to reach people through audio and video VoIP calls. When it comes to call quality and clarity, Facebook Messenger gets two enthusiastic thumbs up; however, the app has also been criticised by some for being a “battery drainer.”

FaceTime
Pre-installed and free to use, FaceTime is one of the best features included on all iPhones and iPads (messaging isn’t included as there’s a separate iMessenger app on iDevices). The only catch? The person you’re trying to call also needs an iPhone or iPad.

Google Hangouts
If you use Google Android, you’ll already have a Google Hangouts account, which syncs seamlessly to your Gmail account as well (bonus: it’s also available for Apple devices). Google Hangouts may have started life as a chat service, but offers good-quality VoIP calls as well as a video chat option. Even better? You can call “any phone number in the world” for free, or at low rates. So the next time you’re stranded in the Himalayas on your mum’s birthday, this is the app to try…

GrooVe IP
With GrooVe IP, you can make VoIP calls and send messages. You can also call landline and mobile numbers directly, by purchasing or earning credits.

While a free version is available, you can also pay for an upgraded version without ads. This one only works on Android devices like the latest from Samsung or Huawei.

Snapchat
Funky filters are only part of what everyone’s favourite social app has to offer: you can also chat to your pals via video chat, call them using the app and leave voice and video messages. Now there is no conceivable reason for you to ever stop using Snapchat. Ever. The video chatting also works with Snap’s fab new Lenses.

KakaoTalk
If you can’t handle a convo without cute and cuddly emoticons, then this is the app for you. It also allows you to make
individual and group VoIP calls, send messages and schedule appointments.

Signal Private Messenger
Signal is all about privacy: with a large focus on data protection, the app uses an advanced end-to-end encryption protocol for calls made and messages sent. You don’t need to set up a separate user profile as the app integrates with your phone number and address book. So if you want your calls and messages to self-destruct without a trail like a Mission: Impossible doc, this is the VoIP app to use. Promise we won’t tell.

Skype
The fact that “skyping” is now a recognised verb in English jargon should tell you about the ubiquity of this app, but there were many who gave up on it after trying a decade ago (those jittery calls!) Not to fear, this VoIP pioneer continues to innovate, with crystal-clear audio and video connections regardless of whether you’re calling London or Lomé. Recently, Skype has started letting users chat via text and make voice and video calls without signing up for an account, or you can use your Facebook or Microsoft account to sign in.

The best bit? You can also call people who don’t have Skype on their landlines or mobile numbers by purchasing credits. If you use VoIP for work, there’s also a separate Skype for Business app (formerly Lync 2013). And if you’ve ever thought of having a VoIP party, this is the app: you can now call up to 25 people at the same time with Skype.

Slack
Anyone who’s ever had to work together on a project with different teams (all based in different locations, of course) knows that Slack can be a true lifesaver. In addition to the existing messaging and file sharing options, VoIP calls were added to the app recently, so expect even more people to get on the Slack express in 2017.

Viber
With more than 800 million users worldwide and high-quality audio, Viber is one of the most popular and highest-rated VoIP and messaging apps. Viber-to-Viber audio and video calls are free, and you can purchase credits to call landlines and mobiles. Many users see it as a perfect combination of Skype and WhatsApp, with fun extras like stickers, doodles, and unique emoticons… if you’re into that kind of thing. Which we are, natch.

Vonage
Easy to install and set up, with Vonage you can make free calls and hold free video chats as well as indulge in all the free texting and group messaging your heart could ever desire.

For a charge, you can also call domestic and international mobile numbers and landlines. In more exciting news, Vonage has been working with IBM’s artificial intelligence system Watson to develop a “unified communications” solution. We’re talking AI, people! Watch. This. Space.

WhatsApp Messenger
Normally just called “WhatsApp,” we’re betting money that you use this one on an hourly basis (or every five minutes, more realistically). One of the best things about WhatsApp is that it continues to evolve: recent developments include the ability to make video calls, added encryption, and our all-time favourite: the ability to send GIFs.*

*There goes any chance of getting any work done for the whole of 2017.

And don’t forget: all Three customers have Three inTouch embedded onto their phones. It’s ideal when there’s no signal indoors, but you still need to make a call over Wi-Fi. Told you we like to #makeitright.

Main pic: Pexels via Alok Sharma