Most critically, is any kind of jailbreaking or exploitation of bugs needed to get builds not released by the manufacturer onto the device?
Yes. What's usually left out of the discussion about Android vs. iPhone's "openness" is that you have to root and unlock your Android phone to install any non-vendor approved operating system mods, just like the iPhone. Here's a good starting point if you want to do this: http://androidandme.com/2010/01/hacks/video-how-to-unlock-an...