Sky Dayton, who had been CEO of the L.A.-based wireless carrier, is replaced by Wohnee Sull, who had been president and COO. Dayton becomes non-executive chairman. He released a statement saying that "Helio has reached a point in its development where I feel the timing is right for this change." Well, there might be a little more to it. Despite some growth in subscribers, the joint venture of EarthLink and Korea's SK Telecom has been losing tons of money. Helio is one of those mobile virtual network operators, or MVNOs, that leases space from existing wireless networks and focuses on distinctive content (sports, entertainment, whatever). Several MVNOs have flamed out in the last year or two (Santa Monica-based Amp'd Mobile was probably the biggest disaster). It's just a very expensive proposition, especially with increasing competition from the wireless carriers.