BtKeyMini is excellent for you if you want to write novels on your iPhone. However it will be hard to cary with you 'cause it a bit big. yes, one advantage is that its wireless, so you don't need to hassle with the wires.
You can put your hands on one for $92. You can see on the picture, thet the iPhone slides in the middle of the keyboard's support. So it's size is like an EEEpc's keyboard.