Is it possible to route my iPhone calls through my MacBook Pro sound system?

There are several bluetooth solutions, that should be useful:

• Phone Amego ($29) - This should do the trick. Works and has interesting features. I recommend it.

• BluePhoneElite 2 - No longer developed and supported. I see almost everything vanished, but I think you should be able to locate a working copy somehow.

Edit: As of OS X 10.10 Yosemite and iOS8 this will be included in the OS itself. It's called Continuity.

ps. I'm not in any way connected to the authors of the software, mentioned in my answer.

Yep this is a new feature included in OS X Yosemite which will be public in Fall 2014.