Sprint offers a discount to companies that use Sprint. If you work for such a company, Sprint offers employees and family members of that employee a discount off of personal cell service. This discount varies with the company depending upon how much usage that company has for Sprint services. (I think UPS is the biggest discount available.)
You can find out if your company is listed by going to any Sprint store or by locating a link on the Sprint website that asks for the email address of the employee. An email is sent to that employee in order to confirm employment. Many companies have this discount, especially the larger ones. I would imagine that much of the public sector employees are also offered discounts.