The problem with confusing these two fields (by the users AND apparently the programmer, Mr. Page) is that when you send SMS with this app, it uses the screen name as ID which if a call back number is used (as you are suggesting one should) then a call back number that is unfamiliar for the receiving end will be shown. In other words, when I am texting someone, I would like them to see my number as GV number, but they see an unknown callback number (to them) which I am forced to use as screen name by your design. When I put my GV number as screen name, of course nothing works even if I have the correct callback number in the forward field. The forward number should be what it says, i.e., callback number. And the screen name should be able to take any string as in username, alias, or at least GV number as a caller ID.