This feature is not on a current W3C standards track, but it is supported on the Firefox OS platform. Although implementations may change in the future and it is not supported widely across browsers, it is suitable for use in code dedicated to Firefox OS apps.
mnc is a read-only property representing the Mobile Network Code (MNC) of the subscriber's home network.
var mnc = navigator.mozMobileConnection.iccInfo.mnc;
Return a number.
Not part of any specification.