I use my piano app on my phone when I don’t have an instrument around to check and make a note of start notes for things we are working on. It can be very handy for any singer to have an entire piano inside your phone! And can really help if you are starting to look at keyboard skills or just want to do some ear training.
To enhance the work you do with a vocal coach, you can also get feedback on your pitching from an array of ‘tuning apps’. This can be a great and affordable way of quickly improving your pitching. I don’t believe that you can easily replace the value of one to one vocal training with an instructor but tuning apps like this can certainly enhance the speed of your development in between lessons
Technology blows my mind a the moment- you can literally hold an entire recording studio in your pocket! In addition to being able to play back for pitching/timing accuracy, it can be really lovely to experience what your singing might sound like with abit of reverb- or some effects and all of this is possible on your phone!