Virgin Mobile USA (NYSE: VM) will now get paid $4.50 for each subscriber it signs on to the Sprint Nextel network between July 1, 2008 and Dec. 31, 2009, reports the Kansas City Star, referencing a document filed with the SEC. Previously, Sprint paid Virgin $2.50 per subscriber, up to a total of $10 million, but the new deal shows just how desperate Sprint is to stop losing customers. The concept of Sprint paying Virgin for each customer it added arose when Virgin bought Helio, the youth-oriented MVNO, and used the event to renegotiate more favorable terms with Sprint (NYSE: S).  At the end of Sept., Virgin had 5.2 million customers, and Sprint had just above 50 million, but has lost millions this year. Virgin also pays Sprint for its wireless network services. Previously, it agreed to pay at least $320 million in 2008, $370 million in 2009, and $420 million in 2010, but the 2008 payment will drop to $318 million.