Consider - an app that replicates this functionality on the phone, but tracks if the user at any point closes the app. This then is reported to the teacher so the teacher knows if there was any cheating.
The "answer given" was just a quote from a teacher about the millions of different ways education is underfunded, and not really about the calculator issue specifically.
Yes, the calculator problem could be solved in a wide variety of methods. Kids needing their own calculators is just one example of how underfunded schools are.