The Wikipedia article for the Lumia 900 lists 'digital compass' among the features of the phone. Likewise the Lumia 900 spec sheet on Nokia's website lists 'Compass (Magnetometer Sensor)' as a feature.
Therefore the answer to my question would seem to be "yes", but when I install certain apps from the marketplace (such as the new PhotoSynth app), I get a compatibility warning:
Some features in this app might not work because your phone does not have: compass
So which is it? Does this phone have a compass or not? Or maybe there's more than one right answer?