This thread has been super helpful to me, so I registered to let you all know what I figured out.
I have VVX-450s and VVX-250s that I'm setting up with G Suite Google Voice.
They all had the default Poly firmware so I needed to convert them to OBi, and I wanted the latest version and the background updating enabled. 6.4.1.1 is the latest version, but I believe you can only get this version via automatic updates. If you don't enable automatic updates, you may be stuck at 6.4.1.0. I haven't tried though.
First step was to login to phone and update to 6.4.0.2 OBi firmware. Note that the Poly firmware requires an https login, otherwise you'll get an error.
Updating firmware to 6.4.0.2 is done as described above using
https://www.obitalk.com/VVX-OE/6.4.0.2/release.xmlAt this point there is no need to use the 6.4.1.0 but you can if you want to.
https://www.obitalk.com/VVX-OE/6.4.1.0/release.xml doesn't seem to work though. And while
https://www.obitalk.com/VVX-OE/6.4.1.1/release.xml does work, the phone got stuck in an endless reboot cycle so I wouldn't use that.
Once the phone restarts (several times) you will log in again using the IP address. At this point you have to use http, if you try to use https you'll get an error. The default username/password is admin/admin.
Now you have to enable the background updating. This requires a .fw file, and will not work with a .xml file or a .sip.ld file. (If you do want background updating disabled, go here to get the .sip.ld file
https://support.polycom.com/content/support/north-america/usa/en/support/voice/business-ip-phones/vvx450-obi-edition.html)
Once logged in to the phone, go to System Management -> Auto Provisioning.
Uncheck the Method field and set it to System Start. Uncheck the FirmwareURL field and paste this URL:
https://downloads.polycom.com/voice/obi/6-4-1-0/,bgu-conv=enableMake sure to include the ",bgu-conv=enable" as this is what tells the phone to enable background updating for future firmware updates. (And the comma is important!)
Hit Submit to save the changes. You can reload that page to make sure the changes are saved.
Click Reboot in the upper right of the browser window. The phone will reboot at least 2-3 times. Once to update to 6.4.1.1, once to enable background updating (the splash screen will say "Conversion in progress, do not power off!"). Eventually once it stops rebooting, you can log in to the phone again and check the Status -> System Status page to see the firmware is 6.4.1.1 and the BackgroundUpdate field says "Enabled".