mga 3D.iso can be played by the NMT, at least in the R300 Pro, it will see the stream being played as 3D, but if it senses my display is 2D, it will play the 2D.
you can also force it to display out 2D via the menu button that you can call during playback, so you simply switch.
you (i think) can switch 2D movies to simulated 3D via the same menu button.