As of 2015, manuals for the Motorola NVG589 model are available at SetupRouter.com. Guides are available that explain how to log in to the router, how to set up Wi-Fi, and how to change the IP address. There is also a general administrator's handbook available from Intermedia.net.
The administrator's handbook for the Motorola NVG589 covers many topics, such as various aspects of device configuration, troubleshooting, using command line interfaces, and technical specifications about the router.
In addition to the administrator's handbook, SetupRouter.com also has a page with a list of screenshots used as part of the router setup and maintenance. Sample screenshots include wireless setup, voice status, software version, troubleshooting and system information.