There's a detailed section in the Owner's Manual that describes all the features and capabilities of Bluetooth. Bluetooth has many features and capabilities - I believe there are 20 pages of instructions describing all the features. There are various commands to access the features in your cell phone, but I don't remember them offhand. I believe the command is "Voice" for voice pass-thru, but I'm not sure.
Of course, you can store all your favorite numbers in the Bluetooth / Onstar Address Book. These are called Nametags and they are very easy to store. Just say "Store" and it will prompt you for the phone number and a Nametag. It takes all of 20 seconds to store a number. When you want to call one of these numbers, just say "Call" and the nametag you want to call.
i.e. "Call Home".