I'm designing a registration page for a portal which which will be used all over Europe. Users have to provide their phone number.
A user can select their country / country code via a drop list, and enter their phone number in a text field.
My question is how to best indicate the format I want the user to enter for the number - area code respectively without the (0).
Alternative 1: Add a text field label which shows an example (Please use the following format: (030) 123456789)
Alternative 2: Prefill the text field with a zero.