You can setup an URL per token to notify each SMS status change, this webhook will notify using POST and having the next JSON schema within the payload request.
{
"id": "5889b9a0710e94066d49dcf1",
"clientId": null,
"to": "+34666000000",
"code": 0,
"status": "delivered",
"createdAt": "2017-01-26T09:56:00+0100",
"eventAt": "2017-01-26T09:57:01+0100"
}
Possible status and status Code can be found in Status Codes