Not really; this is the Open-AT section.
Open-AT is the framework that allows you to embed applications within the modem:
sierrawireless.com/productsa … framework/
You are just using plain AT Commands.
Can you provide a link to describe what, exactly, that is
What “HMI software”, exactly
Again, a link would help.
Do you get any error messages
The commands for sending SMS should be standard - but it’s possible that the mystery “HMI software” is relying upon other specific features of the “TANGO 864-2” …
You’re going to have to do some more investigation to find where exactly the process is failing…