I had a Cingular account that I finally refused to pay. I had asked back in September 2005 that my corporate account be closed. I continued to pay my bills as I was guaranteed the account would be closed, of course that employee has long left the company, so I just quit paying.
Since this was a corporate account Cingular couldn't close it without authorization from my company. So, I figured the best way to cancel was to not pay.
I have not used 1 single minute on that account since September of last year, probably June 2005.