Although there are tons of things that an industry-standard smartphone can do but iPhone can't but for starters we shall consider the ability to pair the device with a Bluetooth Keyboard.

However, this can now be done thanks to a utility named The iPhone Bluetooth Keyboard driver that allows to use a Bluetooth keyboard with the iPhone and iPod Touch. Of course this must be noted that the iPhone must be Jailbroken in order to use this application.
For users who have a lot of problem using the virtual keyboard on the iPhone (and trust me! the number is large), they can simply pair their iPhone with a Bluetooth keyboard and write long emails all they want, or take notes or even write blog posts. The driver runs on the iPhone 3G(S) and all iPod touch devices with Bluetooth support.
The following keyboards have been tested to work as of now:
- Apple Bluetooth keyboard
- Think Outside Stowaway Universal keyboard
- Palm Wireless keyboard
A demo version of this utility is available on Cydia named Keyboard Driver Demo (package details) but it limits the use of the Bluetooth keyboard only within the running app. A full version will be available in Cydia before Christmas and shall support Bluetooth keyboard pairing across all apps. More details on the usage can be found here.