The customer service interaction at most companies is viewed as a reactive experience that typically is related to a pre-sale inquiry or a post-sale problem.
If your organization doesn't see every customer service interaction (both positive and negative) as an oppportunity to generate new business, you're missing the boat.
An unhappy customer who's hairy problem is validated and resolved, becomes your next loyal customer telling your company story for you.
If you want everyone on the phone thinking about how they can sell more to every customer, incent them to do so.
Reward your customer service reps for both their ability to take care of the customer AND their ability to generate business.