If your mp3 is copy protected and your calculator bypasses that copy protection, it is in fact illegal (in the US)
Such a translation would be "format shifting" which is protected under US/UK law (IANAL).
There is no such thing as an mp3 being copy protected. A game on a cartridge is not "copy protected" either.
Such a translation would be "format shifting" which is protected under US/UK law (IANAL).