1.BBM
Although limited to BlackBerry phones, BBM provides for text, audio, video and image transfers in real-time with delivery and read receipts. For it to work, you have to add selected contacts to your BBM list using their BBM PIN.
2.ChatON
Made by Samsung and initially only meant only for their Android & Bada phones, this messaging client is now available for other Android smartphones, iOS and BlackBerry. It offers multimedia transfer, group chat and animated messages.
3.iMessage
This one only works on Apple iPhone and iPad for sending text and images. A desktop client for the same is included in the new version of MAC OS X (Mountain Lion) and a beta version of the desktop client is available for download at http://goo.gl/4Q6DH.
4.Pinch
Pinch not only works on smartphones but also on feature phones (either with a Java app or through a WAP browser). Pinch has also tied up with Airtel to offer Pinch2SMS — from an Airtel number, you can send free SMS to anyone using Pinch.
5.WhatsApp
Available for almost all smartphones (other than Bada and Meego), it works in the same way as BBM and even provides delivery and read receipts. All your phonebook contacts who use WhatsApp are automatically added to your contact list.
