You're right, it is different, & a carefull look will show quite a number of differences.
I also recall now that somebody had said that there were two of them, so this must be the other.
I don't believe that there was a fleet of them but the one I drove came with its own trailer & a truck to haul it was seconded from somewhere whenever they moved it to another area. It's home base was either Sydney or Canberra whenever it wasn't being used.
When the first of the press button phones were released they had ten buttons only. It was at least a year before the twelve button version became available & it may have been even longer.
This one must be the 'new & improved' model.