I just had to send an email out to one of my voluntary clients. We decided on 8 hours a month and she never used me. It was so irritating. Here's a copy of my email. I hope that this helps someone when you're weighing that hard decision. (it was easier for me since it was voluntary!)
Hello xx,
As of October 10, 2008 our voluntary services agreement between xx and Elite Business Services has expired. We have decided not to renew this contract. There was a lack of communication between both parties and we feel that our services would be better used with another business. If you feel you would like to take advantage of our services we would have to be contracted at an hourly rate.
We wish you well in all your endeavors.