Well Nokia is famous for its "production machine", the factories can crank out devices in huge volumes (and low manufacturing costs) so I wonder what is the problem there. It has to be that AT&T has underestimated the demand and is not prepared to restock their supplies?

It might be that they are reluctant to take too many in the beginning as previous Lumia models sold so bad, maybe they are afraid they will have unmoveable stock at their hands later?