I'm pretty sure I said no when that happened, and I can't find a setting anywhere, yet that page definitely has numbers that weren't put on Facebook by the owner. I wonder if the HTC Facebook integration (I have a Droid Incredible, and I knew that there was phonebook integration in the other direction--friends show up in my phonebook if their number is on facebook even if I've never directly added them). It's possible that they either automatically did the sync or asked in a not very clear way when I first set up my phone and was dying to click through all the prompts so I could use it.