Idroid for Idevice
The guys over at Main Page - iDroidWiki have got a working version of Android running 2.2.1 Froyo ported to multiple Idevices. now you can run a double boot Iphone or Ipod touch with both Ios an Android os. Recently it just got better, now you can install everything straight from the Idevice threw Idroids very own repo on Cydia. they are currently working on getting the 3gs, Iphone4, an Ipad working properly. The proses is still an early release an so it is still buggy but the goal is to have a smooth working android os to replace the Idevice Ios
this currently works on 4.1 an bellow.
I got it (Android on my iPhone EDGE) , OK it's a really great improvement but sincerely I can't use it the battery go down in a sec.
Cool. I have an android device and loving it. Although the project is kind or pointless because iOS runs perfectly already