Here is my first google search:
http://www.google.com/search?hl=en&source=hp&q=keyboard+for+iphone+bluetooth&aq=f&aqi=&aql=&oq=&gs_rfai=
The keyboard described in this breathless article seems not to have arrived, but one can always hope for the future.
http://www.appletell.com/apple/comment/a-bluetooth-keyboard-for-the-iphone/
The bottom line is that you have to "jailbreak" the phone to install a keyboard app, Apple will not allow installation of the bluetooth layers for keyboard interfacing. Here is a google search on the most popular hack:
http://www.google.com/search?hl=en&q=keyboard+for+iphone+bluetooth+BTStack&aq=f&aqi=&aql=&oq=&gs_rfai=
Here is a painstaking tutorial on how to download and install the hack:
http://www.iphonehacks.com/2010/01/how-to-use-a-bluetooth-keyboard-with-your-iphone.html
