I've had this for a while, developed by someone else. It's quite handy as I don't want to be opening my Twitter client all the time to check when I have an @reply. It's especially useful when I don't have any data connection and I can still carry out Twitter conversations via SMS
Makes sense, and cheaper for you. Are you hitting a limit as to the number of API requests you can post? I had someone try it out and I didn't receive a DM, but maybe it was because they put a period after my name.