That actually depends. I have T-mobile with the "MyFaves" that allows me unlimited calls to 5 numbers of my choosing. I setup my Google Voice number as one of those 5, so I can initiate an outgoing call from the web interface and it will ring my phone from my Google Voice number, and when I answer it will connect me to the person I was calling.
It's somewhat of a sneaky bypass, but it works great. I know that Verizon and some other cell carriers have similar "freebie" plans where you can select a few numbers to have unlimited calls with. Look into it and you can definitely use Google Voice without using your minutes.