A Mobile Virtual Network Operator (MVNO) is a mobile operator that does not own its own spectrum and usually does not have its own network infrastructure. Instead, MVNO's have business arrangements with traditional mobile operators to buy minutes of use (MOU) for sale to their own customers.
To date, MVNO's are mostly a European, GSM phenomenon. With many simple resellers in the United States gaining popularity, it is likely that the concept will catch on in the US and other parts of the world as well for the Mobile Virtual Network Operator (MVNO).
There is a distinction between MVNOs and service providers, who purchase wholesale mobile minutes and resell to end-users. Normally they do not have their own SIM cards and the services provided by service providers depend on the services of the hosting MNOs or MVNOs.