code: def extensions(self):
          
          if self._extensions is None:
              self._extensions = AssignedAddOnExtensionList(
                  self._version,
                  account_sid=self._solution['account_sid'],
                  resource_sid=self._solution['resource_sid'],
                  assigned_add_on_sid=self._solution['sid'],
              )
          return self._extensions
docs: Access the extensions
  
          :returns: twilio.rest.api.v2010.account.incoming_phone_number.assigned_add_on.assigned_add_on_extension.AssignedAddOnExtensionList
          :rtype: twilio.rest.api.v2010.account.incoming_phone_number.assigned_add_on.assigned_add_on_extension.AssignedAddOnExtensionList