Skype is clearly one of the best chat programs ever created. It has a simple and elegant interface and it is very flexible. You can use skype for normal chatting and for making calls. You can make video calls to other skype user using your internet connection and you can make calls to phones all around the world, for a small price.
The newest of smart phones have interfaces that are very easy to use and can make sending and receiving text messages can feel a lot like chatting. When driving, it is much safer to not have to fumble with the phone to send and receive text messages. DriveSafe.ly takes over this task for you, by reading the text messages aloud and sending replies.