It is possible to replace the idle screen on Yealink phones with the image of your choice. The phones must be using firmware version .70 or higher.
Use the following override parameters in the SkySwitch Provisioning Server:
Background Idle Image
The following override will set a custom background image on a Yealink phone. You must host the image on your own server.
phone_setting.backgrounds="Config:phone.png" wallpaper_upload.url="http://yourdomain.com/phone.png"
Note: Replace 'phone.png' with the name of your image file.