Viber is a text messaging app that was designed initially for smartphones. They expanded to the desktop and feature an Ubuntu client as well. With Viber you can make free calls and send free texts, stickers, photos, voice and video messages to other Viber users, on any device, in any network and country. Its pretty cool.
Viber automatically detects which of your contacts already have Viber, so all you need to do is select a name and start a conversation. No invites. No hassle.
With Viber's user-friendly interface, you can easily send messages and make calls. You can also change your profile picture, identify which of your contacts already have Viber, and see who else has recently joined.
Some of the Viber features... free text, photo and video messages with location-sharing, best-quality VoIP calls using 3G or WiFi, call non-Viber mobile or landline numbers at low rates with Viber out, group messaging with up to 100 friends, no registration, passwords or invitations required. It also lets you download "stickers" which are kinda fun.
I use Viber a lot since most of my friends and colleagues are on it.
Head over to Viber and download the DEB file and install it! That simple!