Sending SMS programmatically without opening message app

You can send messages from your application through this:

public void sendSMS(String phoneNo, String msg) {
    try {      
        SmsManager smsManager = SmsManager.getDefault();
        smsManager.sendTextMessage(phoneNo, null, msg, null, null);    
        Toast.makeText(getApplicationContext(), "Message Sent",
                Toast.LENGTH_LONG).show();
    } catch (Exception ex) {
        Toast.makeText(getApplicationContext(),ex.getMessage().toString(),
                Toast.LENGTH_LONG).show();
        ex.printStackTrace();
    } 
}

Also, you need to give SEND_SMS permission in AndroidManifest.xml to send a message

<uses-permission android:name="android.permission.SEND_SMS" />