The great thing about them is that people tend to read them and they also respond. This starts a great interaction. It gives you a chance to talk to your customers or prospects and efficiently discus your products and/or services.

Yes it is time consuming, but in a way it is also customer service and a great tool for feedback and can also be used for opinion gathering.

There are many companies that sell contact numbers to many interest groups, or just starting one through your banner or email promotion is always a possibility.