I solved my problem in this way
backfavorites = new Command("Back",Command.BACK,0);
favlistelement = new List("Favorites:", List.IMPLICIT);
favlistelement.append("Incoming 1", null);
favlistelement.append("Incoming 2", null);
favlistelement.append("Incoming 3", null);
favlistelement.addCommand(backfavorites);
favlistelement.setCommandListener(this);
I was trying to add listeners, command to my Form variable but I tried to add these to my list element variable thus it was solved.
To show in screen:
disp.setCurrent(favlistelement);