I'm hoping that at least half of C.E.'s would be able to make that logical deduction given their knowledge on ints and the possible lengths of a phone number. :)
You will typically normalize telephone numbers when storing them, that means prefixing them with their national code and two leading zeroes or a plus sign if you want to be fancy. Neither a plus sign, nor double leading zeroes lend to storing as an integer. Even if you're not fancy and normalize your number, there are numbers that have leading zeroes.