When i switched from blackberry to android, BBM was the only thing that I missed. My friends and I have tried a few different services, but the one we like so far is Beluga. It pushes messages to your phone and allows for group chats with added features like sending pictures. The only problem is that it only supports iphone and android, not blackberry.
2007 335i Coupe - Jet Black / Coral Red / Aluminum Trim / 6MT / Sport / Premium / CA / Navi / iPod + USB