Virgin Mobile's distinction of being the first MVNO in the U.S. means it is the "granddaddy" of virtual operators, at least stateside. Enough bragging time has now gone by apparently, as Virgin Mobile has filed for an initial public offering (IPO). The move will take the company public where shares of the company will be traded in the U.S. marketplace. Some pundits believe this signals a maturation of the MVNO segment in the U.S. wireless landscape, but don't tell that to the scrappy folks at Amp'd Mobile or Helio, will ya? Anyhoo, Virgin Mobile has filed to be listed as "VM" on the New York Stock Exchange and it's possible the company will raise up to $100 million in the offering. That wad of cash will most likely be used to pay off debt and give a certain, unknown sum to Sprint Nextel, the carrier representing the American half of the joint venture -- the other half, of course, being Virgin proper.