I don't have a calculator, but I don't use my phone for the purpose. I rarely need to do math away from home, and I use Excel or Calc on my computer at home all the time (especially to work out puzzles in the Q&A by Calculus-Geometry). However, I think few people need calculators. There are some exams where you can't take a phone in, and you will need a calculator - usually with limited functions. Also, specialty calculators - financial or advanced math - might go beyond SmartPhone app functions or be easier to use. I'm not sure.