Exhibit 1: A comparison of the two phones. While not entirely 1:1, essential elements--like the sharing of the ARM Cortex A8 processor and 16M colors--are there. Though the screen on the N900 is resistive, so is the screen on the HTC Tattoo, and they've already committed to releasing Android 2.0. Which leads me to...

Exhibit 2: Droid GSM ROM dump. If nothing can be useful here for the N900, you can bet the nice folks at XDA will do something similar for the Tattoo.

Exhibit 3: "I have just committed the remaining puzzle piece of N900 bootmenu". There's the selector.

Although admittedly this is all theoretical, what's missing to get these pieces together (aside from time)?