code: def sip(self):
          
          if self._sip is None:
              self._sip = SipList(self._version, account_sid=self._solution['sid'], )
          return self._sip
docs: Access the sip
  
          :returns: twilio.rest.api.v2010.account.sip.SipList
          :rtype: twilio.rest.api.v2010.account.sip.SipList