It was a big promise: unlimited data, without quotes, throttling or restrictions. Sprint CEO Dan Hesse has repeatedly defended the company's pledge to offer a true unlimited plan, but now the company is quietly eating its words. Customers on Sprint, Virgin Mobile USA and Boost Mobile have all started receiving text messages warning them that heavy users will be subject to data "prioritization" next month in order to "provide more customers with a high quality data experience during heavy usage times." This prioritization (read: throttling) will only apply to the top 5 percent of data users and only in "congested areas," however, and Sprint tells FierceWireless that users will only experience limited speeds if they're connected to a congested cell site. A small concession to your unlimited data plan -- and one without a defined data cap -- but a small asterisk is still an asterisk.