True, but there are users with their own personal accounts that get their company email on their phones. It still means a call to their company support for the setup. The IT person calls for help from the AT&T support.

Then there are users who have a personal line and a company assigned phone. Two phones. The company phone is still set up by the IT department support for exchange email sync, associated security software. A Sprint, Tmo or VZW might take X minutes to set up and if it takes 3X minutes (3 times longer) to download the drivers for sideloading through ADB or Android Central's Sideload Wonder Machine and add the software for an AT&T phone, the company IT could refuse to use AT&T android phones.