LiveProfile

LiveProfile is an alternative to WhatsApp that allows you to send messages to all of your contacts for free through the Internet - as long as you have an active WiFi or 3G connection.

The app goes beyond just messaging, with Twitter and Facebook integration, status updates, customizable avatars, and other features.

In theory, the messages that you send through this service shouldn't take longer than a second to arrive at their destination. You can see the exact time that the message was sent, when it arrived, and, more importantly, when it was read.

LiveProfile is one of the best instant messaging apps available. It's not as widespread as the legendary WhatsApp, but it has been designed with many quality features that should encourage you to give it a chance.