It’s been rumored for years, and Facebook has routinely denied it, but today it seems clear by the invite that their entering the mobile space in one way or another.
Though, I am a little weary when companies make comments like this one comment quoted from Tech Crunch:
With deeper control of a modified operating system would come huge opportunities to collect data on its users. Facebook knows that who you SMS and call are important indicators of who your closest friends are. Its own version of Android could give it that info, which could be used to refine everything from what content you’re shown in the news feed to which friends faces are used in ads you see.
Notice the first sentence?