The SMS report will show a number of different statuses, depending on the result of the send to your recipients. You can view information about the different statuses below.
This statistic is the number of messages that were delivered to the gateway. A delivered status is basically the letter you put in the letter box at the post office. You know it's on it's way to the recipient, but it might not have reached them yet.
A Contact will be flagged as Acknowledged if they have replied to your SMS, or if their handset has acknowledged receipt of the message. This does not necessarily mean that the SMS has been opened or read; this type of data is not available via the SMS protocol.
In some instances, the recipient's carrier won't use an acknowledgment protocol. If this is the case, the report will only show 'Delivered' for these contacts, even if it was received by the recipients handset.
This statistic is the number of messages that were not forwarded on to the mobile device by the Carrier (e.g. Optus, Telstra).