I knew there was a reason I was keeping my old Think Outside Stowaway Bluetooth keyboard from my Windows Mobile days. Windows Mobile and for that matter Blackberry and Palm had Bluetooth keyboard profiles in 2005. Apple has finally implemented the keyboard profile for both the iPad and now the iPhone.
The Apple keyboard profile is compatible with the Think Outside (acquired by iGo) StoweAway keyboard.
Here is a picture of my 5 row Bluetooth keyboard paired to my iPhone 4. The fn + key don't seem to work which makes sense but otherwise it is fully functional. There is also a smaller 4 row keyboard which is available on eBay northwards of $170. It has crossed my mind to sell it but I like the portability.