I called Google yesterday after getting an email regarding Engage as I was curious about it. I mentioned this thread. He said that as an agency, I should think about joining Google Engage. He basically said that I could represent myself as being an Adwords partner by doing so. I guess that's what Yellowbook is doing, they just happened to send an email to a client of yours. Although I don't like the way they made themselves pass off as Google itself. I guess time to use similar soliciting tactics as this business is starting to become more cut-throat it seems.