Talkray!

WhatsApp Messenger is a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for iPhone, BlackBerry, Android, Windows Phone and Nokia and yes, those phones can all message each other! Because WhatsApp Messenger uses the same internet data plan that you use for email and web browsing, there is no cost to message and stay in touch with your friends.

With Viber, everyone in the world can connect. Freely. More than 460 million Viber users text, make HD-quality phone and video calls, and send photo and video messages worldwide over WiFi or 3G - for free. Viber Out can be used to make calls to non-Viber landlines and mobile numbers at low rates. Viber is available for many smartphones and platforms.

Facebook Messenger is a faster way to message. Reach friends right on their phones, get and send messages fast, message everyone at once and more.

Google Voice gives you one number for all your phones, voicemail organized in an email format, free US long distance calls, low rates on international calls, and many free calling features, including transcripts, call blocking, call screening, conference calling, SMS, and more.

Yahoo! Messenger is an instant messaging client developed by Yahoo! inc. for real-time communication of its users. It provides text chat, file transfer up to 2GB. conversations with audio and video, games. It also supports International Calling, Phone in Number and sending free SMS like Skype.

Zulip is a group chat app.

Nimbuzz offers limited availablility free calls and limited availability free text messaging for users via 3G and WiFi. Calls to other Nimbuzz users are free. PAY to call mobile or landline phones for as little as $0.02/minute in bulk with NimbuzzOut. Free SIP to SIP calls.