gistfile1.js

// known mcc/mnc values for our sim card (this is Telenor Norway)
var mcc = 242;
var mnc = 01;

// First get the sim card number (API supports multi sim phones)
var simNum = Array.slice(window.navigator.mozMobileConnections)
    .reduce(function(current, connection, i) {
    if (connection && connection.data && connection.data.network) {
      // For ONCE we're actually using type coercion as it's meant here!
      if (connection.data.network.mcc == mcc &&
          connection.data.network.mnc == mnc) {
        return i;
      }
    }
    return current;
  }, -1);

// Then get the current APN settings we want to change
window.navigator.mozSettings.createLock().get('ril.data.apnSettings').onsuccess = function() {
  // Mutate current setting
  var apnSettings = this.result['ril.data.apnSettings'];
  apnSettings[simNum] = {
    apn: 'starenttest',
    carrier: 'custom',
    types: ['default']
  };
  window.navigator.mozSettings.createLock().set({'ril.data.apnSettings': apnSettings}).onsuccess = function() {
    // turn data off and on again, giving it time to do so
    window.navigator.mozSettings.createLock().set({'ril.data.enabled': false});
    setTimeout(function() {
      window.navigator.mozSettings.createLock().set({'ril.data.enabled': true});
    }, 5000);
  };
}