I just learned why they won't use droid. The software is open source and not secure enough for them.
It is open source, but Apple is no more secure.
To each their own I guess.
Back to your original question... I haven't used a new Blackberry so I can't vouch but I would probably grudgingly go for the iPhone on AT&T if my work was paying.
I had heard rumors that Verizon would unlock the GSM chip on the iPhone 4S but my quick internet search says no.
Of course, it depends on what you need the phone for. If it's just email and text and phone and contacts and calendar, stick with Verizon and a new Blackberry. If the web and more smartphone savvy apps are more your thing, go for the iPhone.