iPhone as bear repellent? Uh, no thanks.
Look, I don't know from brown bears, but here in the eastern part of the country, you generally aren't going to see any bears. Black bears are skittish, generally afraid of people, and don't do the kind of territorial bluffing attacks that you hear about out west.
If you do see a black bear, and it's coming at you, that's because it's half-crazed from hunger and you look tasty. The only way your iPhone is going to do any good at that point is if you can somehow wedge it in the critter's jaws to impede its chewing.
Alternatively, depending on how long the batteries last while playing the "bear scaring app", it could act as an audio beacon to help searchers find your gnawed remains.
(H/T to Maddened Fowl.)