.DELIVERY REPORT STATUS REASONS

STATUSREASON
DELIVEREDThe message was delivered to a cell phone.
SUBMITTEDMessages were operated by the operator for delivery.
PENDINGCould be delivered but the status of the message is not yet available.
EXPIREDYour message validity period has expired. This happens when the destination mobile is either switched off or out of the coverage area for a certain period of time. The SMSC failed to deliver even after its final attempt as per its retry scheme
UNDELIVEREDYour message was not delivered. This happens when the Carrier encounters
  1. inactive or unidentified or untraceable destination mobile number
  2. mobile handset memory or inbox full
  3. no credit balance is available to receive the SMS Text message (specifically for pre-paid or pay-as-you-go)
REJECTEDYour message was rejected at the SMSC of the Carrier. This happens when the destination network is not available or blocked to the Carrier