If you have a Mac, you can register for free and download the XCode with an iPhone emulator included at http://developer.apple.com/. They also have several basic program examples and tutorials that should help you decide if it would be easy enough to make your app. If you do decide to do it, you then need to pay $99 to get a developer certificate and the ability to distribute the app to actual phones.

With no knowledge of Mac programming, I took one of their example apps as a base and made a small utility program for work in about half a day, including the time it took to figure out the certificates and provisioning setup.

And you might want to hold off on the 3G upgrade. Popular rumors are pointing to a new iPhone announcement in June again, and even if the new model doesn't interest you, the market will probably be full of cheep used 3G phones at that point.