https://www.obitalk.com/info/documents/admin_guide/OBiPhoneAdminGuide.pdf page 284 mentions "ScreenSaverType" and "ScreenSaverPictureURL". Description of the latter includes:
"When SceenSaverType is Slide
Show (Specified URL Only), this
parameter specifies the URL to get the
pictures for the slide show. It can be a
http:// or https:// url to get the screen
save picture(s), or the absolute path of an
internal folder to get the screen saver
pictures. If http url is used, the server may
indicate 'no-cache' in the Cache-Control
header of the http response to the phone
to force the phone to download a fresh
picture from the server on every screen
picture refresh."
Thus it seems that if you have a server preparing a suitable weather info image the ObiPhone can be configured to display it as a screensaver. I have not tried this.
Probably the image should be the same size and type as for background pictures. Page 170 of the above document.
Searching for 'background image', 'background picture' etc in that document may lead to useful information.
