Yahoo! Mobile offers free Yahoo! push email and instant messenger integration with Blackberry mobile devices.

Yahoo! Mobile for Blackberry includes:

-Yahoo! Mail is pushed automatically to your BlackBerry device
-One-way synchronization between your BlackBerry device and your web based Yahoo! Mail account. When you make changes on your BlackBerry device, it’s reflected in your web account. Two-way sync is coming soon)

To setup Yahoo! Mobile Email for Blackberry, visit Discover Blackberry. Where prompted in the Integrating Email Accounts section of the set-up instructions to Add Account, simply add your Yahoo! Mail account details.

Yahoo! also provides free instant messaging service on Blackberry with features such as:

-Emoticons,
-Stealth-mode
-Knowing when someone is typing

Visit Blackberry.com to download the free Yahoo! Messenger for Blackberry