So you're thinking of upgrading to an iPhone 4 and iOS4 just so you can take advantage of the new iMovie app, which will only run on the new hardware/software combo?
Not so fast, say the hackers at Redmond Pie, who offer up the above video. First of all, if you've upgraded your (jailbroken) iPhone 3GS/3G or iPod Touch to iOS4, iMovie will run on it, and run quite well, too. All you have to do modify the info.plist file, changing the "Minimum system version" to "3.0.0" and "front-facing-camera" to "false." One caveat: exporting your project to a video larger than 360p is not working in this hack.
Attempts to get similar results using 3.1.2 or 3.1.3 firmware have so far been unsuccessful.