Vodafone just released version 4.5 of the Blackberry OS. This version, while posted on the Vodafone site, can be downloaded and installed to most Blackberry Pearl’s (Update: see the links at the bottom that I just added which will allow you to download the 8300 OS or the 8800 OS upgrades). PC Magazine has a pretty good overview of the new features in version 4.5 - including voice notes, streaming media support, bluetooth stereo music, Microsoft Office document editing with DocumentsToGo. Even though these versions are from the Vodafone site, they will work on any carrier’s Blackberry. Just make sure you select the proper model Blackberry to upgrade and follow the instructions from the link below. UPDATE: If you are on T-Mobile - do not use the instructions below - you should wait until the official T-Mobile OS is released. Make a backup before doing any upgrades and follow the instructions on the Blackberryforums site explicitly.

Link: Vodafone Blackberry 8100 version 4.5 OS
Link: Instructions on installing the version 4.5 OS to your Blackberry 8100 (Pearl)
Link: Blackberry Curve - 8300 OS upgrade to v4.5
Link: Blackberry 8800 - OS upgrade to v4.5