Retail is one. Any retail company that doesn't have a legacy system to integrate with uses iPhones and iPads for their POS systems.

Logistics is another. According to an ex-girlfriend who works in LTL, the logistics industry is 90% people with iPads and iPhones. The only people who aren't using mobile devices for their "real work" are people like her who are chained to a desk doing back office stuff.

Tradesmen is another. When my water heater burst, the water heater guys, the plumber, the guys who replaced the floor, the guy from the gas company, and the guys who replaced the walls all took pictures of the situation before, during, and after to document what they did. Copies went to me, to the landlord, and to their office.

It's like carrying around a whole office's worth of office equipment in your pocket. It's a document scanner, you can use it to measure stuff, to get paperwork signed, to take pictures and look at them later, it's a level or flashlight in a pinch, you can load reference materials on it, and on and on, and that's without getting into really specialized software or peripherals that let you do all kinds of cools stuff.