I think that it was the right thing to do from a short-term business perspective, but bad from a public relations point of view.
Sprint "fired" customers who were calling the company's customer service line too often. This makes sense from a business perspective because these customers were using up too much of the company's resources. This could harm the firm's ability to make a profit.
On the other hand, this is probably a bad move in the long run because it makes Sprint look like it does not care about its customers, which is a major problem with the image of many companies these days. It seems like Sprint should have taken a less drastic step like charging a fee to those who call more than a specific number of times per month.