The Square POS terminals using tablets (it is iPads?) that rotate for you to sign are nice. I especially like how they'll automatically email you a receipt, which is great for reimbursements or filing taxes because it means I don't need to scan anything.

I've never been impressed with anything using a cell phone though. It's too clunky of an experience. I get that it might be useful for farmer's market and other very small retail situations, but when I'm going into a retail store, a real POS terminal is better.