this is the official post if you try one of these share your feeling about it and tell us about Advantages/Disadvantages like what happen to the original firmware on your phone .....every thing work ok or not so we can know the best one to try

openmoko.com
http://qtopia.net
The Qtopia application platform for embedded Linux — Trolltech
OpenMoko booting on E6
Qtopia on Rokr E6
Install OpenMoko or Qtopia in Rokr E6 or A1200