Since your devices have USB host capabilities, would it be possible to connect a Windows Mobile, or Windows Mobile Smartphone device (which are slaves) to your drive in order to access photos on the drive from the phone and display them with the phone's jpeg reader?
It's not host capability. It is USB device capability.
If your phone work as USB host, then it can access Nexto as a normal USB HDD.
But Nexto need lot of power from USB, so you need to connect power adapter to Nexto.