I was looking at the Home Depot Twitter Account ( http://twitter.com/homedepot ) and I noticed that its tweets are tagged as follows:
about 2 hours ago via web by sarahsambuca
How can I achieve this functionality for my business twitter accounts?
You will notice that this is a business account, and that it is "verified".
One of the features of verified accounts is "Allow contributors so multiple people can tweet from your account".
You can find out more on twitters own website, but this service is in beta and is not generaly available yet.
This servie is due to be rolled out this year I think...