"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 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.
In addition to basic messaging iPhone, Android and BlackBerry WhatsApp Messenger users can send each other unlimited images, video and audio media messages".
This isn't nearly as feature rich as Handcent but it has more features than anything else Ive used thats free.
If anyone knows of any other text apps please feel free to chime in.