I downloaded and copy to usb device an application.
When I connected the usb device to the phone, I saw at the storage section the the phone recognized the device, but didn't find the application.
How can I mount the app from the device and install it on the DX?
Make sure under Settings/Security that Unknown Sources is enabled. This could be locked by the administrator:
I was able to place an .apk on a USB drive, plug it into the DX650 and install the app, by using third party file manager (Astro) to browse to the .apk and 'launch' it choosing the Package Manager.