Hi I am no expert but managed to run Android for a few months from SD on my hd2 easily then made it the primary os, it was easy and worked well. Since Christmas I've been running WP7 with no problems at all, I phoned MS and told them I needed an activation code for my HD7 and they give me it :-) Once you find a good guide to follow the whole process becomes quite easy, I think I followed a tutorial on youtube. XDA forum is brilliant but takes a lot of reading. It is possible to have the phone dual boot WP7 and Android from a partition on the sd card. I LOVE my hd2 because of the amount of tweeking i've done on it