That 4am booty text is meant for one set of eyes only, but there's a good chance your fling's not the only person seeing it the next morning; try your boss. That's why Apple just added a feature that alerts you to your employer monitoring your company iPhone.
In its latest iOS 9.3 update, Apple will show you when an iPhone is being accessed by another party on both the Lock Screen and the "About" page of settings, which means you definitely won't miss it. According to 9to5 Mac, you'll see a highly obvious, "‘This iPhone is managed by your organization" on the bottom of the locked screen and the "About" page will even go so far as to clarify exactly what aspects of the device are being monitored.
Now sure, this doesn't stop anyone from checking up on you, but the goal here is to increase transparency, and remind employees that a manager can access a company phone. If you take issue with this, well, you can just suck it up and pay for you cell phone yourself. Ya know, texters can't be choosers. Or something.