My 8320 came with AIM preinstalled back in January...
I think he is referring to the new version of AIM that you can download from BlackBerry web site - - I did the upgrade from the version that came on my Curve when it was new and I still had 4.2 running on the Curve - the new version of AIM would not work on that OS - - but when I upgraded to the T-Mobile 4.5 OS the new version of AIM worked just fine.
go to tmobiles website and download the 4.5. i did 2 nights ago. took about an hour to do. i also got the new aim, and its rad. way better than the one installed on it