MVNO is a tough business. Essentially, you are leasing some network bandwidth from a major wireless telecom, yet, you have to find a niche or provide some competitive edge over the mobile-land-lords. Some MVNOs have come and gone, such as the Disney and ESPN mobile, while a few remains (ie. Virgin, Helio, Boost) but have not made as much of a splash as it should. I ran across another MVNO today called KDDI Mobile which runs over Sprint's network. This company is targeting specifically to Japanese folks living in America. It offers short terms (monthly) or long term (annually) subscriptions which allows both domestic and Japanese calling plans. Its biggest selling point offering services in both English and Japanese (customer service, stores, communications, etc.).
As mentioned earlier, KDDI Mobile is using Spring's CDMA network, which is quite similar to its operation in Japan. They offer a limited amount of LG/Sanyo handsets which runs on Japanese language, which is its big selling point).
KDDI offers three voice subscriber plans (small 200min, medium 650min and large 1,200min) priced at $30-$50-$70 per month. They also have a pre-paid plan which charged $0.12/min on calls and $0.15/text on top of a daily $0.10 service charge. Because it is catered towards Japanese visitors, signing up doesn't require any social security number or deposit. All you need is to have a valid passport and credit card. Its advertising and marketing is very low-keyed; perhaps this is why they can sustain as a business; by just targeting directly at its niche demographic (whereas Helio and Virgin is trying to take on the main stream customers amongst AT&T, Tmobile, Verizon and Spring).