Virgin Mobile has just launched as an MNVO in Mexico.
The tariff structure is surprisingly simple (for Mexico):
2 pesos (15 US cent, 11 Euro cent) for 1 minute talk time to anyone in Mexico, USA or Canada
2 pesos (15 US cent, 11 Euro cent) to send an SMS to anyone in the world
2 pesos (15 US cent, 11 Euro cent) for 1 MB of data
https://www.virginmobile.mx/es/tarifa/