Connecting to COM serial port through USB with Putty I am trying to use my android phone connected to my PC as an SMS gateway by executing AT commands.

I have attached the phone to the PC (Windows 7), and device manager shows that it is in COM4 port. I opened PUTTY in administrator mode and tried connecting to COM4 but it just shows a black screen with the green cursor but won't let me type anything.

I tried playing around with the values of "Local Echo" and "Local Line Editing" as I found in one of the suggestions in another question here, but the best I can get (set both to "Force On"), I can type stuff on Putty but it doesn't really do anything.

Any suggestions?
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.