For these reasons, I can't see retailers embracing Square's app combo and throwing out their cash registers. But for businesses that make fewer, and more expensive transactions (and who have a smartphone-equipped, credit card-loving customer base), Square's Register and Card Case apps could be very handy. Square will be accepting tabs for additional merchants in the coming weeks, and you can sign up for more details here.
Square also makes a tiny, plastic credit card reader that plugs into the headphone jack of a smartphone or tablet--just in case your customers want to pay with their credit cards, the old-fashioned way. The credit card reader is free, but Square takes 2.75% of each transaction.
While Square's new Card Case app doesn't mark the end of the cash register era, it is a big step in mobile device transactions--until we see NFC implemented in a big way, it's the only app that really lets people pay with their phones.