Comcast Not Able to Deliver Business Grade Service - How Do I Get out of the Contract?

In 4 years with AT&T my phones were never out. In about 18 months I have had a second complete outage of phone service. Each time its several hours and costing me hundreds of dollars in lost revenue. Has anyone left there term contract in the middle of it? If so, how did you do it. I cannot afford to continue with Comcast.