Bug 11209 introduces the functionnality not to send multiple SMS with the same content to the same borrower in one day. As it is the expected behavior, the status of duplicate notices should not be set to 'failed' but to 'cancelled' or 'duplicate', to make the difference with notices that really failed and maybe have a specific treatment (send again, phone call, etc...)
*** This bug has been marked as a duplicate of bug 14723 ***