It is a big setback for BlackBerry which is trying to retain its base of corporate clients and government agencies while getting new customers.
It had been thought that the launch of a revamped line of smartphones powered by its reengineered BlackBerry 10 operating system was crucial in doing that.
Home Depot's defection sent BlackBerry shares tumbling which is a bit weird because there were also reports that its Z10 device made a strong debut in the United Arab Emirates which would have been worth a few more sales than Home Depot.
In fact, the devices have been well received in Britain and Canada, and have not been launched in the US yet.
Stephen Holmes, a spokesman for Home Depot, refused to tell Reuters when the outfit had made up its mind or whether the decision was made before or after the launch of the BlackBerry 10.
The numbers of phones used by executives is rather small.
The company makes extensive use of 60,000 rugged Motorola smartphones used by Home Depot's store employees. Those devices provide mobile point-of-sale, analytical, walkie-talkie and traditional telephony services.