It's in the Catalog - it's Free - and after September 30th, you won't be able to tweet without it. 

In June a new version of the Twitter app became available in the Sidekick Download Catalog. Twitter made updates to their service and to remain compatible, we’ve made some behind-the-scenes changes to the Twitter application for Sidekick.  Download the latest (free) version now to keep your Twitter app up-to-date. After September 30th users will no longer be able to log-in with the older versions. 

Install the latest version of Twitter in these easy steps:

1.      From the Download Catalog, select the Applications folder.

2.      Go to Social & Community

3.      Choose Twitter (You will see the upgrade arrow next to the title if you have an older version of the application.)

4.      Select Upgrade, and the newest version of the application will begin downloading.

5.      When download is complete, you will see the Ready to Install window. Select “Install” (or “Install and Restart” for Sidekick Slide users) to complete the process. 

6.      You’re done!