Once upon a time I worked for a company that largely marketed its products through direct response advertising. The company had a robust call center that took product orders, returns and customer queries. My first day on the job (working in marketing), my boss sent me to the call center to monitor calls. At the time it seemed like an odd place for me to start my training, but an hour later I realized just how perfect it was. I knew all about customer perceptions of our advertising, key drivers toward purchase and frequently asked questions. While by no means an expert in the company's products and practices, I learned a lot just by listening to the voice of the customer.
The call center is a hotbed of data and customer insights, and if your marketing department isn't utlizing the wealth of information your call center holds, invite them down for an hour of monitoring. Focus groups cost thousands of dollars (and are limited to a relatively small test group) but your customers are usually more than willing to let you know what they think of your company and products merely for the hope that they'll be able to impact the system.
Don't get me wrong - I'm not saying that traditional marketing methods have no purpose, but the call center should be a key part of campaign development. Particulary with the rise of social media, marketing and the call center will be working more closely than ever - and the two departments should see just how symbiotic the relationship can be.