NumberKey Connect lets your iPhone act as the number pad for your Mac; particularly useful for Apple's wireless Bluetooth and laptop keyboards, which lack number keys.
Another excellent example of computer-to-iPhone interaction is NumberKey Connect (US$1.99) from Balmuda, which allows the iPhone to act as a Mac's number pad.
The software works in tandem with a small program running on your Mac (this computer-specific software is Mac-only as of press time, supporting both Intel- and PPC-based Macs) and like Remote, it utilizes Apple's Bonjour service-discovery networking protocol.
NumberKey Connect makes a perfect companion to Apple's wireless Bluetooth and laptop keyboards, which lack number keys. It even offers four different themes, and its behind-the-scenes use of Bonjour translates to an automatic and reliable connection for your Macs running 10.5.5 and above, with an iPhone 2.1 or later. Simple in form and execution, this solution is both infinitely useful and potentially prophetic concerning future device interaction.
Of course, there's always full-on computer control, and for that you can use the free Mocha VNC Lite . As long as there's a wireless network connection -- including 3G signal -- and a properly configured Mac or PC, you can access your computer and control it as if you were in front of it, all from your iPhone.
The software provides support for all sorts of interaction using gestures and taps, including different input modes for controlling the screen or for manipulating icons on the computer.
For my part, I've used Mocha a few times to access mission-critical servers, allowing me to input commands via Mocha's on-screen keyboard remotely and helping me avoid a very bad day. At home, I use the software for accessing the Mac that controls my optical disk carousels. With Mocha and some not-so-fancy AppleScript, I can access the Mac to pick one of several hundred movie titles without having to interrupt the current program on screen.
My own examples are just scratching the surface as to what can be done with the ability to control a computer from anywhere you are.
Clearly, these are the first steps for the iPhone in device interactivity. Although the pairing of two wholly different devices to perform a specific task isn't anything new to the computer scene, the iPhone's software platform and wireless connectivity options portend an almost endless array of possibilities.