From what ive read its where you use "services" that in some way are connected with the internet. Its just a service to let the get money from you. I read online that they charge you like 3 cents for each one but that might of been a long time ago so they might of went up.
GOOD LUCK
I just found this on sprint.com
PCS Vision (Data) Services: Services require a Vision-enabled PCS Phone or device and are not available while roaming off the Sprint Nationwide PCS Network. Data usage is calculated on a per kilobyte basis. If you have not selected a PCS Vision Pack, you will be charged a casual usage rate of $.01 for each kilobyte when accessing PCS Vision. Data usage is rounded up to the next whole kilobyte. Rounding occurs at the end of each session or each clock hour and, at that time, we will deduct accumulated data usage from your plan, or assess overage or casual usage charges. You are responsible for all data activity from and to your phone/device, regardless of who initiates the activity. You will be charged for partial/interrupted data downloads, including data that is automatically resent, and for unsuccessful attempts to reach websites, use applications or services. As long as you are logged on the Sprint Nationwide PCS Network, you will incur data usage charges. Additional data is used in transporting and routing on our network, and data may be automatically resent due to interrupted or partial downloads. For this and other reasons, estimates of data usage will vary from actual use. In certain instances, we may delete premium and non-premium items downloaded to available storage areas (e.g., personal vault), including any pictures, games, ringers or screen savers. Your invoice will not separately identify the number of kilobytes attributable to your use of specific sites, sessions or services used. Downloading or use of Premium Services are generally not included with PCS Vision access. We provide no warranties and make no representations or claims with regard to any content provided by a third party.