You don't need to eat into your minutes allowance or spend extra money to make phone calls with these apps - perfect for calling friends and family over Christmas.
When you take out a phone contract you're paying for four things - texts, minutes, data and the cost of the phone. The majority of the cost is down to how much data you want.
Most network providers are happy to give you unlimited texts and enough free minutes for a small call centre. They do this because people are using WhatsApp and Facebook Messenger to send free messages using tiny amounts of data or over wi-fi.
There are a range of apps that allow you to make calls in the same way. They may not seem as useful now that providers give away free minutes like sweets on Halloween, but calling over wi-fi has other benefits. You can make free calls to family and friends abroad, which could be particularly handy over the festive season, and it means you can make calls wherever you have wi-fi, even if your phone signal is non-existent.
Before you make an international call, bear in mind that there are a few countries where making phone calls with these apps is banned. These countries are: Azerbaijan, Belize, China, Iran, Kuwait, Morocco, Oman, Pakistan, Paraguay and UAE. In Saudi Arabia, Skype calls are allowed, but WhatsApp calls aren't. Banned apps will often not work while you are in that country. Always check your destination's restrictions when it comes to messaging and phone calls.
Viber is an all-in-one communications app- text and picture messaging, phone calls and video calls all under one roof. It's designed as a replacement for the suite of communications apps built into your phone. It creates a copy of your contacts and tells you which ones have Viber already.
It's free to call or message anyone who has the Viber app installed, and messages you send are encrypted for privacy. You can call people who aren't Viber users, but you need to buy credit first.
WhatsApp is synonymous with texting and it's so popular that it has all but replaced the word in the same way that Googling something has come to mean searching online.
It's not limited to messaging, though, you can make voice and video calls, too. Like Viber, it creates a copy of your contacts. Anyone without WhatsApp will have an 'invite' icon next to their name, so you can send a message asking them to join.
Unlike Viber, WhatsApp doesn't give you the option to buy credit to make calls to people who don't have the app. But with more than one billion registered users worldwide, there aren't many people not using it.
Skype started out as a desktop chat program on PCs, which used webcams to let people communicate for free. It grew in popularity to the point where Microsoft bought it for £5.2bn (it had previously been owned by eBay and several equity firms).
Now the program is used as much on mobiles as it is on desktops. Thanks to selfie cams, Skype's heritage of face-to-face chatting lives on, but you can make voice calls, too. You can also use it to send messages.
Whereas WhatsApp and Viber are tied to phone numbers, Skype works through your Microsoft account. You can search Skype's vast directory of users using real names, user names and phone numbers. This means you could feasibly connect with anyone. Don't worry, you don't have to accept contacts from strangers and it's up to you how much information is displayed on your account.
Messaging isn't the end of Facebook Messenger's talents - you can make phone and video calls with it, too.
You and the recipient will need a Facebook account, but you don't need to be Facebook friends. Anyone can initiate a chat with you, but you need to accept that request before they can start talking to you.
As the name suggest, FaceTime is predominantly used for video calling, but you can make voice calls on it too.
It's an Apple-only app, though, so you can only call other iPhone users.