I've been told that my speedometer cannot be calibrated because its AWD. True?

Most speedo shops that are certified can only do two wheel drive. A performance shop with a four wheel dyno may be apply to check the accuracy of you speedo. The only reason it would be off is incorrect tire size. There are plent of speedometer apps for smartphones that use GPS or Garmin Nuvi GPS tells you the speed limit of the road you're on and how fast you are going. I don't know if these options are acceptible for the courts.