ATR has done NXT truck trial models to good success. ATR's chassis design is really very good and his specific knowledge in getting his mobile phone to operate the bluetooth remote is key. An aspect that ruled this out for me.
I found it easier, quicker and cheaper to make my own 4 speed remote gearbox using 2 sequentially operated PF m motor switched gearboxes.
see http://www.brickshelf.com/cgi-bin/gallery.cgi?f=390250