While I cannot speculate on Microsoft purpose of a 411 service, I think it is pretty obvious why google dumped theirs - they now have access to an enormous source of human speech through google voice.
Yeah. The voicemail transcription feature truly is like an open invitation to provide them with real-world data across a wide range of accents, phones, and people.
More so, it's not a very good business to be in. The same functionality at a much, much higher profit margin is in smart phones, and that's where you want to put your effort because it has such a higher rate of return.