Teltonika has an awesome function to do that without AT commands.
You can send it directly by the browser via HTTP. Go to: Services / SMS Gateway / Enable and create a user/pass.
Then you can send SMS just like this:
https://192.168.1.1/cgi-bin/sms_send?username=user1&password=user_pass&number=9111111&text=testmessage
or.. if you want an automated system, use CURL on Windows or linux to post those commands automaticaly.