If your employer required the use of a smartphone for essential components of your job and provided you with a smartphone and cellular data plan, would you not use that smartphone for those components of your job?
I'd not use employer- or government-furnished equipment for tasks that the equipment wasn't provided to complete, but I'd definitely use it for those tasks.
Exactly. Bank needs me to have an official FruitPhone to access my account? Fine, send me the phone, I'll turn it on when I need to bank, and at all other times it sits powered-off in a drawer. Same for the government-supplied DroidPhone I need to access my Social Security statements (or whatever). Turn on, do my business, turn off.