For better search results, the correct spelling is “Concatenated” 8)
What did you try?
What was the result?
As I understand it, Concatenated SMS works by using PDU mode, and adding a header to each of the “sub” messages?
So, the first thing you need to do is to determine exactly how your “Concatenated SMS” service works.
Then, as far as AT commands are concerned, it’s just a matter of sending the appropriately-formatted messages in PDU mode, isn’t it?