Basically this was introduced for Android Marshmallow to support "3gpp" for GSM/UMTS/LTE messages in 3GPP format or "3gpp2" for CDMA/LTE messages in 3GPP2 format.
Here is the full example for SMSReceiver:
public class SMSReceiver extends BroadcastReceiver {
public void onReceive(Context context, Intent intent)
{
Bundle myBundle = intent.getExtras();
SmsMessage [] messages = null;
String strMessage = "";
if (myBundle != null)
{
Object [] pdus = (Object[]) myBundle.get("pdus");
messages = new SmsMessage[pdus.length];
for (int i = 0; i < messages.length; i++)
{
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
String format = myBundle.getString("format");
messages[i] = SmsMessage.createFromPdu((byte[]) pdus[i], format);
}
else {
messages[i] = SmsMessage.createFromPdu((byte[]) pdus[i]);
}
strMessage += "SMS From: " + messages[i].getOriginatingAddress();
strMessage += " : ";
strMessage += messages[i].getMessageBody();
strMessage += "\n";
}
Log.e("SMS", strMessage);
Toast.makeText(context, strMessage, Toast.LENGTH_SHORT).show();
}
}
}