This isnt the full story...
Actually... According to Sprint the official number is someone who calls in 15 times in one month... Not just over a duration of 6 months, ect...
Also, each "call" to Sprint can be recorded as many many more than just 1 call... Each time you get transfered to a different department its counted as 1 call, each time you speak to a supervisor thats another call, ect ect... So if you have an issue and that rep passes you off to another rep, you essentially called sprint 2 times, even though you didnt.
Also, its not just the people calling in for free credits... There are a few that were canceled because of Sprint's incompitence. They were overcharging this person for a long time (about 6 months IIRC). Each time they would call in and attempt to get the issue resolved, they would get transfered a number of times (each time counting as another call, which they werent aware of), eventually they would get the issue resolved, but the next month, Sprint screwed it up again... They ended up sending her a letter telling her that she called in too much and was a problem, find another provider.
Also, if you let your friend use your phone to call Sprint, it counts against YOUR calls (while this makes sense in some respects, every call to Sprint they ask you for your number, which SHOULD mean that the call should count towards the number your calling in about, not the number your calling from)...
So as for this article, it holds some truth, but it doesnt tell the full story, and it doesnt tell about the legitimate problems people have with Sprint and how they are getting screwed because of Sprints inability to unscrew themselves...