Can a Mac be set up to dial arbitrary numbers by connecting to an iPhone? I normaly listen to music on my iPhone while working, and regularly I also have to be able to make calls. 

What tends to happen is that I google for the contact details of the place I'm calling and then have to type the number into my phone. It stikes me that there is probably a much more effective way of doing this - is there a utility that either lets me select a number on my browser and automatically call it? Or even just a shared clipboard between my phone and my MacBook?
I use Google Voice's service to have my computer ring a third number and call my iPhone. Since I have most contacts in my Address Book and don't mind adding new ones - iCloud will get most contacts to the phone and Siri does a nice job dialing things, but there are also software packages that will literally dial your iPhone over a bluetooth connection.

Check out Dialectic for starters if you want a tool cut exactly for the job of dialing from OS X to iPhone remotely.