The text message is far from dead, but smartphone apps that let you chat with others (whether via text, video or voice) without charging you for every single message are increasingly popular. We've rounded up five of the most popular choices.
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There are two important points to make regarding free messaging apps. The first is that in order to use them, both you and the person you're communicating with need to have the app installed. For that reason alone, they're unlikely to ever completely replace conventional SMS/text messaging, which works on any mobile with a SIM card in it. One recent study suggests almost half of us use them, but virtually everyone doing so sends ordinary text messages as well.
The second point is that 'free' is a somewhat deceptive term. Most of these apps are free to install (WhatsApp being the exception) and you don't pay for each individual message, but you do pay for the data used. Text messages won't use up large volumes of data, but video chat definitely will. If you're using a Wi-Fi connection at home or in the office, that won't matter, but it's potentially a problem if your smartphone plan doesn't offer a large amount of data. (It also may provide a good reason to avoid these apps when you're overseas, since roaming charges can make the process ridiculously expensive.) If you make voice calls to a non-connected user via their phone number, you'll also pay fixed rates, which may or may not be cheaper than using your actual phone for the same caller. Check carefully.
iMessage (for chatting) and Facetime (for video calling) are technically separate apps, but both come standardly preinstalled as part of modern versions of iOS and Mac OS X so we're treating them as a single entity. If you run an entirely Apple shop and that also applies to most of your friends, both are robust and easy-to-use platforms that are, as you'd expect, deeply integrated into the OS. However, the lack of options for any other platform means that this is unlikely to be the only solution you use. FaceTime doesn't work over 3G on older iPhone models unless you jailbreak, but can be used with the iPhone 4S and iPhone 5.
WhatsApp appears to be the most popular of the alternative messaging applications, something that's in part attributable to the huge range of platforms it supports. Apps are available for iOS, Android, BlackBerry, Windows Phone 7 and Symbian. On all these platforms, the main feature set is the same: you can send messages, audio and video to individuals or groups. The WhatsApp app itself isn't free — you'll pay $0.99 a year to use it, with the first year free on most platforms apart from iOS — but the upside is there are no ads involved.
The main direct rival for WhatsApp, Viber has an even broader range of platforms covered, including iOS, Android, BlackBerry, Windows Phone 7, Symbian and even Bada. The apps are free and there's no advertising or ongoing charges (which does make you wonder how the company will ever make money).
Facebook maintains apps for every major phone platform (check out the iOS, Android, Windows Phone 7 and BlackBerry clients), and makes it easy to chat both real-time and disconnected with anyone on your friends list. That makes it potentially very useful for chatting with those close to you, but it's not an option you'll ever use for one-time communications. At least you won't have to talk someone into install a single-purpose chatting app, though, since the chances are if they're a Facebook user they'll already have the app for other purposes. (Facebook also offers separate messaging-only apps on several platforms if you want a less distracted experience.)
While you might think of Skype as a desktop app, there are plenty of mobile versions available as well, with native clients for iOS, iPad, Android, Windows Phone 7 and Symbian. With more than 660 million users registered worldwide, there's also a fair chance someone you want to talk with has a Skype account. Both video calling and messaging are supported, though Skype definitely puts its emphasis on the former.
This is a competitive space, and there are lots of other good alternatives. Honourable mentions go to BlackBerry Messenger, which pioneered the notion of free text chat across the same platform and remains a great alternative for BlackBerry owners; Google+, which offers well-designed video chat through its Hangouts; and fring, the only other chat platform to register in most market surveys.
Want to sing the praises of another free messaging option? Tell us about it in the comments.