4.0 has not been released for the 7290 yet. The 7290's run v3.8 that basically is 4.0 as far as I can tell. It has the same base features that 4.0 does on the 7280 without the Enterprise Activation feature.
the carriers actually have 4.0 for the 7290. It's version 18.104.22.168 I believe (might be 172 I'll have to look when I get to work). They are just internally testing it and then will brand it with their own version numbers and release it shortly.
I have Cingular 3.8 on my 7290 and it has two addresses under each contact (home and work). What I don't have is the password wallet or whatever it is called. I am looking forword to getting that and my IT department being able to wirelessly provision our new units.
I want to install 4.0 on my ATTWS 7280. I am a little worried of something going wrong - and my corp IS dept has told me they don't support it yet so if something goes wrong I am on my own (even though ATT has released it).
If I do upgrade and something goes wrong - can I go back to the 3.7 (or whatever version) I now have? What other risks are there?