'Validation of a value
@param value: the value
@return: tuple (value, error), where error is None if value
is valid.'

def __call__(self, value):

    value = value.strip()
    if (value[0] == unichr(8206)):
        value = value[1:]
    number = s3_str(value)
    (number, error) = s3_phone_requires(number)
    if (not error):
        return (number, None)
    error_message = self.error_message
    if (not error_message):
        error_message = current.T('Enter    a    valid    phone    number')
    return (value, error_message)
