Ad-supported mobile operator Blyk was literally yesterday’s news. Today sees the launch of yet another company, ThePudding, offering a free mobile service paid for by advertising searches that come out of keywords picked up from your voice calls. ThePudding says it will take these and deliver relevant advertising and mobile content to your phone. The company says its technology will also work on VoIP and other voice-based calling services.

Since Pudding is only in testing mode, it’s not clear how exactly it would function on a mobile—eg, would the ads come as SMS and MMS, or as voice calls, or all of the above? VentureBeat did a couple of run-throughs and came up with a very hit-and-miss set of responses including some very unintended racy content (Pudding claims it is parent-proof); if you go to the site you can see how it works for yourself.

There is another potential pitfall with the service: privacy concerns over how one’s discussion can be tracked. Of course, Pudding’s founders insist that data culled from calls won’t get used anywhere beyond its system for delivering relevant advertising and content. Google (NSDQ: GOOG) has faced similar questions over privacy, but it has managed to rise above this to create a multi-billion dollar business from serving ads based on keywords. (This carrot is perhaps what has motivated Pudding’s backers, which include Opus Capital putting up $3.5 million in May 2007.) It wouldn’t be too far-fetched to see Google trying to integrate such a voice-based ad-serving system into the G-Phone that everyone loves to speculate about.

It’s worth pointing out here that for now Blyk is not planning to deliver ads based on the content of a user’s voice calls, preferring to stick to other ways of profiling its users.