Seth Godin discusses tech support: "When someone calls tech support, are you viewing it as a chance to do something for them, or to get rid of them to cut costs? ..... One of the reasons small is so much more important than big is that people who think small have the power and flexibility to do things for their customers."
Every touch with your customer - billing, install, tech support, admin - is a chance to turn them into an evangelist, to make them indifferent, or to lose them.
Do all your employees have a script that says something like this: "Thank you for being our customer. Did we resolve your issue?"
Then after a Yes, you can upsell or cross-sell like this: "Mr. Jones, I see your email address is email@example.com. Would you be interested in getting a personalized email, like firstname.lastname@example.org?"