Phone Amego is a great application that monitors your compatible Bluetooth cellphone and notifies you of a incoming call via a popup window on your Mac. This window displays the caller's phone number, and if the contact is in your Mac's built in Address Book, the window will display the callers name, phone number and photo. In conjunction with Google Voice, you can initiate calls within Address Book without having to dial the number on your cell phone. Simply click on "work" or "home" to the left of the phone number and select "Dial with Phone Amego" or "SMS with Phone Amego". This Snow Leopard compatible application resides in your menu bar where you can access all of Phone Amego's preferences which includes launching an AppleScript with inputs such as an incoming call, or your cell phone is out of range. I have Phone Amego set up with my Google Voice account and my iPhone. When I get a call I have an AppleScript play a iTunes song that says
"ring... ring... your iPhone is ringing" the song plays through my AirPort Express connected to a whole house speaker system. I didn't find any bugs in the latest build and the developer answers questions promptly. All in all, I highly recommend this app!