It depends, if you are signing up on a mobile device (say creating an account as part of an Android device setup) it is absolutely required in my direct experience with no way to bypass it.
However if you create a new account via a desktop browser, it's not been required.
for your first account, it is not required. once they think you are opening more than one, or they think you may be a bit, a working non-voip humber is required.