Once a message is successfully accepted by the carriers, it will reach them. Delivery is out of SMSGlobal's control once this happens.
It is then the responsibility of the upstream carrier to deliver the SMS to the destination handset and send back the delivery receipt information to SMSGlobal.
If your message has a status of sent, delivered or undelivered, in general, you will be charged for the message.
If your message is not accepted by the upstream carriers (for example, due to an invalid number), you will not be charged for the messages.
For more information, please refer to these articles: