Virgin buying Helio, but why?

The FT reports that Virgin Mobile USA has agreed in principle to buy out SK Telecom’s losing US venture, Helio. Both are MVNOs (i.e. virtual operators) that run on Sprint’s CDMA network. The FT story says Virgin has 5.1 million customers and Helio had not quite 200,000 in January (but has likely been losing customers since then); not surprisingly, the combination will be called Virgin.

Google’ing for other stories on the subject pointed back to the FT report as an exclusive. However, one May story on Silicon Alley saw the combination as complementary, while four days later (i.e. six weeks ago) SK denied that any such discussions were underway.

The thing I can’t figure out: why would Virgin bother? It’s not going to catch the larger carriers (e.g. T-Mobile, with around 30 million subscribers). It’s not going to gain significant scale by increasing its subscriber base by 4%.

I can think of only one possible explanation: money. The deal gives SK a graceful exit from their failed US market entry, and saving face is a big deal for Korea’s largest cellphone operator. I suspect that SK made Virgin a deal they couldn’t refuse: perhaps a cheap price for Helio, perhaps side benefits (such as an investment in) Virgin. The terms will probably show up in a Virgin 10-Q or 10-K sometime down the road.