Virgin Mobile, the Sprint Nextel (NYSE:S) prepaid brand, said it will change its mobile broadband plans to cap subscribers' data throughput speeds if they go over 5 GB of data usage. The new changes will take effect when users' month-to-month plans run out after Feb. 15. Virgin, which has a variety of flat-rate unlimited mobile broadband plans under the Broadband2Go moniker, said it is making the changes to "ensure optimal experience." Such changes are not without precedent; T-Mobile USA and Cricket provider Leap Wireless (NASDAQ:LEAP) introduced similar speed-throttling measures last year. Article