A Mobile Network Code (MNC) is used in combination with a Mobile Country Code (MCC) (also known as a "MCC / MNC tuple") to uniquely identify a mobile phone operator/carrier using the GSM/LTE, CDMA, iDEN, TETRA and UMTS public land mobile networks and some satellite mobile networks. The ITU-T Recommendation E.212 defines mobile country codes.
more : http://en.wikipedia.org/wiki/Mobile_Network_Code