"Today, of course, every last smart phone (even the old pre smartphone mobiles) has a calculator and even has a currency exchange key but they're too lazy to use that."

Calculator, yes. Currency exchange function (in the sense exchange rates are pre-loaded) no.

But most importantly (unless you're a spending manufacturer always needing to do sums on the fly) practice in doing quick calculations - rare.

Roaming data rates and people's further laziness in not setting up data overseas <-- further problem.