import re


def valid_phone(number):
    """
    Simple US phone number validator.

    Valid number must be 7, 10, or 11 numbers depending on country and
    area code inclusion.

    To validate, all non-integers are stripped out and length is measured.
    If a number happens to have a length of 11, the first number must be a 1
    """
    # Initial state of False
    non_digit = re.compile("\D")
    cleaned = non_digit.sub('', number)

    length = len(cleaned)
    if length == 11 and cleaned.startswith("1"):
        return cleaned
    elif length in [10, 7]:
        return cleaned

    # Return the state of validity
    return None