Command your mobile with OS X’s Address Book
Having used a Mac for years, I really didn’t know about this feature until a few weeks ago. A friend of mine has broken his mobile’s keyboard so he can’t dial numbers manually. Sitting on my couch he had to call a friend of his, so he opens up the Address Book on his MacBook, makes a few clicks and his mobile phone starts calling. Wicked.
Try it out: just pair your mobile phone with your Mac’s Bluetooth Preferences, and you are ready to go. Launch Address Book and click on the small Bluetooth icon (which I didn’t notice for years). When the Bluetooth mode is switched on, you can right-click on any phone number to access the context menu with options for dialing or sending SMS messages.

Useful? Hardly. When the Address Book’s Bluetooth mode is on, you also get a popup window on your screen when receiving calls. I’m yet to find out if I can use it for hands free talking.