Many military personal favour the "Balistic-HC" phone case, as it practically turns your phone into an indestructible object.
You could even through it at someone, and it might be considered a lethal weapon!
There is no military regulation that I can find to suggest this case is in anyway a requirement, but considering the harsh conditions the military find themselves in, it's a practical case to have on a mobile device.
Keep in mind that during "basic training", recruits won't be worrying about "luxuries" like cell phones anyway.
