Nimbuzz is a free cross-platform mobile messaging and entertainment app that features unlimited messages, video sharing and data transfers. They also offer discounted international calls to any phone number. Nimbuzz is currently available in BlackBerry World.
Nimbuzz also supports Twitter, Facebook chat, Yahoo Messanger, Gtalk, and more. Use Nimbuzz avatars over any of these systems or hit the Nimbuzz chatrooms to make new friends. Nimbuzz boasts over 100 million users with their cross-platform strategy that 1st party services seem to shy away from.