Definition
MCC/MNC is the pair of codes that identifies a mobile network: the Mobile Country Code (3 digits) identifies the country, and the Mobile Network Code (2 or 3 digits) identifies the operator within it.
The codes are defined in ITU-T Recommendation E.212 and used in 3GPP specifications (TS 23.003) as the first part of the IMSI. Together they form the PLMN identity.
In messaging, MCC/MNC is the standard key for routing and rate cards: an aggregator routes to and prices by MCC/MNC, and HLR or MNP lookups return the MCC/MNC of the operator that currently serves a number.
A country code in a phone number (E.164) is not the same as an MCC. For example, the UAE has calling code +971 and MCC 424; Saudi Arabia has +966 and MCC 420.
Some countries have several MCCs, and operators can hold several MNCs. Always map a number to MCC/MNC through a lookup rather than guessing from its prefix where porting exists.