Ok guys, here is the code:
var materialFace1:BitmapMaterial = new BitmapMaterial( bitmap1.bitmapData );
materialFace1.lightingEnable = true;
var appFace1:Appearance = new Appearance( materialFace1 );
var materialFace2:BitmapMaterial = new BitmapMaterial( bitmap2.bitmapData );
materialFace2.lightingEnable = true;
var appFace2:Appearance = new Appearance( materialFace2 );
var materialFace3:BitmapMaterial = new BitmapMaterial( bitmap3.bitmapData );
materialFace3.lightingEnable = true;
var appFace3:Appearance = new Appearance( materialFace3 );
var materialFace4:BitmapMaterial = new BitmapMaterial( bitmap4.bitmapData );
materialFace4.lightingEnable = true;
var appFace4:Appearance = new Appearance( materialFace4 );
var materialFace5:BitmapMaterial = new BitmapMaterial( bitmap5.bitmapData );
materialFace5.lightingEnable = true;
var appFace5:Appearance = new Appearance( materialFace5 );
var materialFace6:BitmapMaterial = new BitmapMaterial( bitmap6.bitmapData );
materialFace6.lightingEnable = true;
var appFace6:Appearance = new Appearance( materialFace6 );
var box:Box = new Box( "box",100,100,100);
var face:PrimitiveFace = box.getFace(Box.FACE_LEFT);
face.appearance = appFace1;
face = box.getFace(Box.FACE_BOTTOM);
face.appearance = appFace2;
face = box.getFace(Box.FACE_FRONT);
face.appearance = appFace3;
face = box.getFace(Box.FACE_BACK);
face.appearance = appFace4;
face = box.getFace(Box.FACE_RIGHT);
face.appearance = appFace5;
face = box.getFace(Box.FACE_TOP);
face.appearance = appFace6;
This code allows to have a cube with a different texture by face.