In short, LEO's are exempted from all of the "Rules of the Road", with the sole and notable exception being "Due Regard". There are additional restrictions or limitations, on a state-by-state basis, but that's the nickel version.
Now, having said that, here's where I stand on it: As an example, how fast do you / should you drive on the Interstate when in a marked unit, not responding to a call. Do you (a) drive the speed limit; create a 1/2 mile long logjam behind you, and see who's got the cojones to pass you?; (b) drive 10-15 over while every driver you pass says "Look at that arrogant jackwad driving at the same speed he writes tickets for?"; or (c) try to find the happy middle ground where you're not creating a logjam, but not flying by people like Krispy Kreme is about to close? For me, it's (c). I usually run in the 75-80 range on the "I". That seems to work. Anywhere in the 5-7 over range on most roads will usually work. My "line" is usually 15 over (except for School Zones and residential areas), so I'm not doing anything I would stop you for.
Cell phones and MDT's. Most MDT's now have a (GPS) speed-related lockout which disables most functions, usually in the 15 mph area. As for cell phones, hands-free OK, anything else not. I used to tell my guys "Never write a ticket for anything you do on a regular basis." For those who wanted to debate the "LEO exemption", my response was "Well, it ain't illegal to step on a rattlesnake, either...but I don't recall ever seeing you do it." Me being an old fart, I usually pull over anyways for most phone calls, since I'm already multi-tasking by listening to four separate channels on my VHF radio; watching what's going on around me; driving; and now trying to carry on a conversation on the phone. Just too much for my old brain. Pull over, pull off, or let the call wait until you can. I've worked a number of crashes where a cell phone was a contributing factor, sometimes even on a hands-free device.
I try to not do anything, even if the law allows it, that wouldn't sit well with "Joe Average" if they saw me doing it.