Developing a project that uses GM862 Telit module, I have find out that the sms that are not received, goes to the service center, where they are stored and not always are being send back to us when we are reachable! Sometimes these are put in a black-list, other times these are just not being send! The problem is the GSM protocol, it seems it is like a bug! When a terminal reconnects to the network, the network does not notice the reconnection, therefore we must make our presence noticed.
Sending a SMS, one call, or one demand to the network, it will send all the sms pending, back to us!
This is worth also for the regular cellular phones, even if nobody notice this!
At the bottom of the post you will find the link to the FORUM, where the Telit engineers and the Round Solution men's (Harald in primis) have helped me.
It's very strange that, in three years, approximately, of forum, nobody has never posted this problem, and as I have placed the question, hundred of visits on this argument. This tells us more about the trust of the M2M systems in commerce.

http://www.roundsolutions.com/forum/thread.php?threadid=2533

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