Currently, I have the crown in being the fastest typist on a mobile phone device @ 81 wpm (words per minute). The device used was an iPhone 3GS.
Furthermore, to verify this I used an application known as iTextSpeed. I just got it a few days ago, and beware: it's extremely addictive.
I honestly believe that there isn't a faster speed out there at the moment, so I went ahead and submitted this to the Guinness Book of World Records. Hopefully my application will be accepted!
UPDATE: My latest record is now 83 WPM. I'm aiming for 90... and if I get that, then I don't know whats impossible!
You can purchase iTextSpeed from the App Store for $0.99.