def valid_number(phone_number):
    """Valid a cellphone number.

    :param phone_number: Cellphone number.
    :type phone_number: str

    :returns: true if it's a valid cellphone number.
    :rtype: bool
    """
    phone_number = phone_number.replace(" ", "")
    if len(phone_number) != 10:
        return False
    for i in range(10):
        try:
            int(phone_number[i])
        except ValueError:
            return False
    return True