The two companies are both "mobile virtual network operators" who resell Sprint wireless service with their own exclusive phones, applications and plans.

Along with the $39 million stock transaction, Virgin is getting a shot in the arm of $50 million in cash from their partial parent, Virgin Group, and Helio's former part-owner SK Telecom. SK Telecom will now own 17% of Virgin Mobile USA; the Korean company has long wanted a place in the US market, which is why they invested in Helio in the first place.

Acquiring Helio gives Virgin a monthly subscription base to supplement Virgin's prepaid plans, the company said. The acquisition will also apparently drive down Virgin's costs because of some sort of amendment to Virgin's agreement with Sprint, who run Virgin and Helio's physical cell phone network.

We'll learn more throughout the day, including what's going to happen to Helio's phones and customers, and why Helio's part-owner Earthlink seems to have completely vanished.

Helio was announced in 2005 as a high-end, data-centric mobile phone provider that was supposed to bring exclusive Korean phones and a sense of openness to the mobile landscape. But from their very start, they had trouble finding their market and focus. By mid-2006, they had changed into a young-adult focused carrier, and arranged a tie-up with MySpace. They've had several innovative ideas, such as their "buddy beacon" GPS friend-tracking application and their excellent Ocean messaging phone, but they never really gained traction in the marketplace.

To give you an idea of the size of Helio, you can value this purchase at $39 or $89 million, depending on whether you count the Virgin cash infusion. Verizon recently bought Alltel for $5.9 or $27 billion, depending on whether you count the assumption of debt. Yes: Alltel is worth at least 30 Helios.