Those using jailbroken iPhones now have the option to install a new theme called OS X Lion Ultimatum which is said to be the best looking, most accurate and easiest to use OS X port to date. The theme supposedly brings the complete Mac operating system interface to Apple’s popular handset.

The theme was developed by college freshman and ModMyi member Timothy Elliot. In addition to a strikingly similar Mac look and feel, Lion Ultimatum brings a number of Mac features to the iPhone such as mission control, dashboard, a customizable lock screen, Finder menu, launchpad, stacks and draggable windows, just to name a few. The video below showcases several of these features running on Apple’s smartphone.

The app is applied via DreamBoard and will cost you $3.50 in donations to the developer. LifeHacker has the complete installation guide which has been reproduced below.

1. Open Cydia
2. Tap Manage Sources
3. Tap Edit, then Add, then add source fnetdesigns.com/cydia/repo
4. Go to the Changes section and install Theme Outlet
5. Close Cydia, go to your home screen, and open Theme Outlet
6. Browse for OS X Ultimatum and download it from there
7. Open up Dreamboard, browse for the OS X Lion Ultimatum theme, and install it.

While this mod looks extremely impressive, I'm not so sure I'd want such an interface on a small iPhone screen. Should this theme be ported to the iPad and its larger screen, I'd be much more compelled to try it out.