Well I got this a little to late, I saw this post after having AT&T send me two phones, neither of which had the mass storage able to be seen. It was a huge pain. First phone worked, then crapped out, they sent a replacement which didn't work right away, finally my last phone did work. I hate resetting my apps to my new pin.
Posted from my CrackBerry at wapforums.crackberry.com
Excellent, were getting this issue whenever we sent a bold back to RIM for service. My users will be pumped!
AS a side note, when i attempted to install the USB driver, step 1, it said i already had a newer version installed. So i skipped that bit and moved straight to step 2 and it worked a treat!