June 20 - 1:45pm EDT   The mobile virtual network operator (MVNO) market in the US may be on the verge of collapse with Helio about to scale back or shut down entirely, according to a rumor circulated by Engadget. The provider is allegedly telling store managers that it will shut down at least some of its retail shops in possible preparation for a takeover by Virgin Mobile. No information has yet appeared to suggest that Helio is withdrawing support for the service itself. [full story]