Android OS- How is it different from Linux?

Over the course of the next month I will be investigating a few things about the Android OS.  I'm interested specifically in these things:

1. What kinds of guarantee is the operating system making in order to deliver phone calls?
2. Does the Android OS have modified scheduling code, or is it simply leveraging the standard Linux scheduler?
3. Is there anything else unique about the way that Android deals with processes?

Once I've investigated this, I'll be digging into the source and maybe even make my own changes to the OS.  It should be easy to test the Android build using this emulator.

--Colt