Well I can tell you a close friend who works for Verizon (and has a blackberry) got an email last week notifying them a new Desktop manager & OS upgrade was coming in March.
His blackberry has Verizon's OS 3.9 to utilize their Lotus Notes infrastructure. So it may just be 4.0 or 4.1
Also, now that the 8800 is being released next week on the new AT&T, maybe the BIS 4.2 will start getting deployed. I would think each carrier would wait for it to be deployed before doing the 4.2 upgrade. Just my opinion.