It may not be most practical or efficient, but there are some advantages to doing calculations with Siri or Google Now on your smartphone or tablet.
- Other relevant information and representations also given (only on Siri, via Wolfram Alpha)
- Don't have to open a separate app
- Opportunity to judge reasonableness, check answer - if Siri comes up with a value that doesn't make sense, you have to reevaluate how you communicated that calculation.
Is voice search ready to take the place of your students' scientific or graphing calculators? Of course not! It's not even a practical replacement of the calculator app. However, especially with Siri/Wolfram Alpha, I really appreciate that it gives the students information that didn't even ask for. You know, sometimes they might be bored enough to check it out. ;)