Possible reasons for delays or unsuccessful deliveries:

• The cellphone is turned off
• The cellphone memory is temporary full
• The subscriber is temporary absent or without coverage
• The user has terminated the subscription with the mobile operator.

Important notes:
1) The price for unsuccessful and successful deliveries are the same.
2) Final delivery notification is currently supported by GW211, GW220, GW230 and GW250. GW220 has intermediate delivery reports also.

How can you get the delivery notification:

1) Yap protocol
Add Nrq=1 when you send the message

2) Http protocol
Add &Nrq=1 to your http syntax when you send the message

3) Web services
Insert "true" in the Nrq field