Over the weekend, someone used a fire ladder to climb to the roof of a huge warehouse in Willebroek, a Dutch-speaking municipality in the Belgian province of Antwerp, cut a hole in the roof, and made off with 3,000 to 4,000 brand new Apple (AAPL) iPhones, according to reports in the Belgian press.

The crime, believed to be the largest iPhone heist to date, was discovered Monday morning and had the earmarks of an inside job. The hole in the roof was cut directly above the location where the iPhones had been stored. Police have launched an inquiry.

The warehouse belonged to Ceva Logistics, a U.S.-owned transport company with headquarters in the Netherlands. Company officials were reported to be “seriously annoyed” but would not comment.

The iPhones were on their way to Mobistar, Apple’s exclusive Belgian carrier. Mobistar had been having trouble meeting demand for the popular phones, but Patti Verdoodt, a Mobistar spokesperson, told De Standaard that their supplier had been contacted and a new shipment would arrive well in time for the holidays.

“We have the serial numbers of the stolen iPhones block[ed] anyway so they cannot be used,” said Verdoodt (Google translation). But because Belgium is one of only three countries in Europe that sells iPhones without a SIM-lock, that would not prevent the thieves from fencing them for use on another carrier’s network.

There is some disagreement in the Belgian press about how many iPhones were taken. De Standaard put the number at nearly 4,000.  Gazet van Antwerpen put it at more than 3,000. Both papers agreed that the street value of the loss was about 2 million euros ($3 million).

[Follow Philip Elmer-DeWitt on Twitter @philiped]