Big changes may be ahead for the U.S. mobile virtual network operator market, with Virgin Mobile USA reportedly set to acquire Helio-the U.S. operator owned by SK Telecom.

Helio is a joint venture between SK Telekom and Earthlink, with SK Telekom recently becoming the controlling partner. The brand has struggled to take hold in the face of tough competition by the incumbent U.S. operators, and has lost hundreds of millions over the years.

The Financial Times is reporting that Virgin will acquire the Helio service and integrate it under the better-known and more successful Virgin brand. Virgin is also a MVNO, the key attribute of which is that it leases wireless airtime from other network providers rather than building its own network.

Once touted as a revolution in the wireless market, the MVNO strategy has largely proven a failure. The one common thread between the two most high-profile MVNO's - Amp'd and Helio - was their content rich and services heavy offerings. Last year, the youth-oriented Amp'd filed for bankruptcy, and Helio has been on deathwatch every since.

Virgin Mobile is the only MVNO to make any progress, with over 5 million customers on a pay-as-you-go model. Helio has about 200,000 subscribers paying a monthly plan.