Quoth Desk clerk knows all
We once had a guy, who was a stay over in the room, put several hundred dollars in cash inside the phone book for safe keeping. Unfortunately that happened to be the day they took out the old phone books and put in the new ones. The head housekeeper had to go through all the old phone books until she found his money.
Why would the housekeeper be the one who had to go through the phone books? Considering it's not something you'd expect for someone to hide money in a hotel phone book, I'd have been inclined to tell the guest "Here's the pile of old phone books, but we don't know which one is from your room - you're welcome to look through them". Also, what would have happened if the hotel had been more organized, had arranged for a recycling firm to pick up the old books (after all, it's a large chunk newspaper - a grade that's frequently recycled - in a form that's unlikely to be contaminated with any foreign matter other than the covers), and they had already been taken to the plant?