How Big Business Is On Twitter Without Being "On Twitter"

In the past couple of weeks there has been multiple instances where well-known brands have confided in me that they are on Twitter, but not participating.

What, exactly, are they doing if they're on Twitter but don't have an account, are not following anybody and are not tweeting out any sort of content?

They're listening and doing a lot more than just listening.

In fact, a lot of these brands are acting on the customer service-related issues, they're understanding where their competitors are