There are many searchers complaining that the Google Phonebook is not working. A Google Web Search Help thread has some of those complaints.
It does appear to have changed the way it works. Just recently, Vanessa Fox wrote an article named Removing Your Personal Information From Google. In that article, she had a link to a Google Phonebook result for her own name, which showed several Vanessa Fox results, with addresses and phone numbers. Now, if I click on that search result, I don't see any results.
Now, there is nothing.
The thing is, if I knew the specific zip code that person lived in, I can still get phone book results. For example, [vanessa fox, 54661] returns this result:
But a simple search for Phonebook results as done in the past, seemed to have stopped showing phone numbers.
Forum discussion at Google Web Search Help.
Update: Google's JohnMu commented below that the phonebook operator was officially removed today. A Googler posted about this on his personal blog explaining.
Things change, and Google has dropped the phonebook: and rphonebook: operators for finding phone numbers (rphonebook: was for "residential phonebook" and focused on home phones). As you can imagine, this was an endless source of hassles for people (who were surprised to see themselves searchable on Google) and for Google (who had to constantly deal with all of the takedown requests and outraged letters from folks who thought they were unlisted).