Twitter's not likely to replace your call center or email response team, but it could be part of a more effective overall approach to service--and potentially cut down on call and email volume in the process. Done right, it at least gives an otherwise faceless enterprise a chance to show its customers--rather than just tell them—that it cares about keeping them. Take Comcast: the cable giant operates in a business where customer service is a legitimate differentiator--The Discovery Channel is still The Discovery Channel with another provider. Comcast has put an actual face on its Twitter service efforts: Bill Gerth, also known as Comcast Bill. Under the latter moniker, he's something of a minor Internet celebrity, regularly responding via tweet to customer issues.