phones would be enough
I'd just be happy to get my staff off Itunes dependent Iphones, BES dependent blackberries and buggy Android devices. These devices have the current benefit of no killer business app.
On the desktop side, it's still going to depend on what applications your business is addicted two. Nothing for Ubuntu can currently break the Office addition because only MS apps can fully function with current MS file formats. For Exchange, you can get close but your still looking at a user revolt and angry executives. Quickbooks... unless you go to the hosted service.. local Quickbooks is going to keep Windows on your accountant's machines.
You only need to sign off on the invoice for one MS Office or Exchange license to start wishing for anything else with a remotely reasonable price point.