The official release has not been made for the 4.5 OS. It is out in some other places in the world and you can rig it to work on your phone. Not sure if this leads to any issues with features.
Check out
CrackBerry.com – The #1 Site for BlackBerry Users & Abusers or
Pinstack.com- BlackBerry forums - Support discussions, BlackBerry themes, Blackberry software.
Once the official release is made for your phone and your service provider it will be out.
There are tons of upgrades for the 4.5 OS.
While on the subject, I want this phone
