The Voice tab > Phone tab > General > Select Logo: setting controls the logo that is displayed for a few seconds as the phone powers up and is described in the above document.
It looks like you're wanting the Voice tab > Phone tab > General > Select Background Picture: setting which will display as a background/wallpaper image while the phone is operational.
Keep in mind that the background will be partially obscured depending what is currently displayed on the phone during normal use.
Regards,
Patrick---
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