Verizon assured their customers that Motorola would have plenty of DroidXs in supply, but that isn't what happened soon after it launched on July 15th. Customers ordering a new DroidX have been told to wait until August. Verizon's HTC Incredible was already back-ordered, and industry-watchers assumed that some customers would switch to the easier-to-get DroidX.
But shortages of both phones, as well as Sprint's HTC Evo, lead analysts speculating that a component shortage is to blame. Samsung's AMOLED displays are in short supply, so HTC has turned to Sony. The difficult-to-get displays are for 3.7 inch phones, such as the Incredible. Both the Evo and the DroidX have 4.3 inch displays, which may be even more difficult to procure, and would explain why both phones are currently sold out.
Computerworld reports both Amazon, Wirefly and Best Buy have DroidX back-ordered as well, with Amazon now reporting a five to seven week wait.