Google has just been granted a patent from the USPTO that replaces ringback tones with adverts. The idea is to replace the ringback sound you hear when you're calling someone and waiting for them to pick up. The ringback sound that you'd normally have to listen to anyways while you're waiting is replaced by an audio advertisement.
It's a concept that end-users may not appreciate, but carriers and advertisers will be more receptive to for added revenue and exposure. Google being the advertising company that it is will now have another channel to deliver ads, although it's not clear whether it would be a feature implemented through Android or through partnerships with carriers.
The advertising ringback could also be implemented as part of Google Voice, which is a free VoIP calling and voice message management system. The use of audio adverts in the ringback could be justified for sustaining the free service.
[via Unwired View]