The Samsung BlackJack doesn’t come with Java (J2ME/JME/MIDP/JAR/JAD) installed on it. So you can’t just download MXit or Opera Mini or any other Java apps to a Samsung i600.
But there is a way around.
You first need to install a Java MIDP emulator on your Samsung BlackJack device; usually called the JVM. Then you will be able to download any Java JAR/JAD program from your phone’s internet browser. After you have a Java Emulator for your Windows Mobile device, you can go to the mxit wap site www.mxit.co.za/wap and download the Samsung -> “Other” version. It will now work.