I have successfully paired a Bluetooth keyboard with my iPhone 4S, and it works great for composing messages.
However, I can't find a way to send a message from the Messages app using just the keyboard.
I've tried Enter, Alt+Enter, Ctrl+Enter, and Shift+Enter.
There's a thread on Apple's site that covers the same topic - one of the posts alluded to a "send" button on a full-featured iPhone keyboard.
Does anyone know what extended key code or combination the "official" keyboard is sending? If not, is there a way to find out?