Obviously, there are a lot of SMS handlers. Since I don't have SMS set up on my system, I can't reproduce what you are seeing, but I might be able to dig up some info.
What are you seeing? Automated messages coming back when you test inbound?
What is the text in those automated messages?
The only "SMS Send" toolstep instance is in System_OutgoingSMSGenericObject by default. I'm not seeing an automated response, as I go through the handler sequence...but I can't put them in debug to see what is really happening.