Connecting to COM serial port through USB with Putty
You can only do that on phones or 3g devices that are recognized as modems by the os.

I had one Nokia communicator that I used for that and controlled this using at commands.
 Also I had a Sony laptop with a 3g card that could be controlled with at commands and inclusive enable the hidden gps :) 

That Sony still sends his coordinates to my Web server so I know where he has been :) if stolen :) 

You need to check if your hardware is compatible and the OS has the correct driver implementation.