4404 is a mechanical AWD transfer case. It has no low range and automatically switches from RWD to AWD when differential out put shaft speed is sensed between front and rear drive shafts.
4406 is an electronic shift 4x4 transfer case with high and low range 4x4 and hig hrange 4x2. Very similar in operation to the stock ranger / explorer 4405 transfer case, just a hell of alot larger. See pictures on this page:
For other interestes, there are several pages of pictures on that link, as well as this one:
DD: 2010 Sport Trac Adrenalin. 4.6L V8 / AWD with Terra Grapplers and Voxx G-FX wheels.
Toy: 1999 Ranger 4x4 4Door. Replacing 302w 1.5L Kenne Bell with a 351W: Explorer EEC-V DIS, AFR205 heads, custom 1 3/4" long tube headers and Autorotor 2.6L supercharger, intercooled with '03 Cobra and custom fabricated manifold.