Google's primary income source is search advertising, but the company regularly tries to find new sources of income, such as charging companies for the use of its otherwise free online applications or selling access to scanned versions of out-of-print books. Variations on any of these approaches could work with its Voice phone service, which is rumored to soon leave beta status behind. A hint that Google might be leaning towards the advertising model came in the form of a patent filed earlier this week, which describes a method of delivering targeted ads to phone users.

The patent application, called "Ringback Advertising," is assigned to Google. In general terms, it describes a system for delivering ads to any sort of phone system, including IP, cellular, or landline phones. The idea is to place software somewhere within the flow of telephony data that can identify when a given call is not active, then request audio ads for delivery during that time. Although this obviously pairs nicely with Google's Voice service, there's no reason it couldn't be rolled out to telcos that choose to partner with the search giant.

The patent identifies three specific times that ads might be appropriate: when a caller is dialing, when the call is suspended via call waiting, and when the call is placed on hold. That last one might be a bit problematic for many companies, which seem to enthusiastically advertise themselves during hold times.

One of the methods for targeting advertisements may also go over poorly with the companies at the other end of the line. Google plans, in part, on using the number that was dialed to choose which ads to serve during the call. If the system works like Google's search ads, it's possible that a competitor could buy up time in a category that would see its ads served up while a customer is placed on hold. There's a certain poetic justice to that, but it's doubtful that businesses would see it as tolerable.

The ads can also be targeted based on information about the person doing the dialing, such as geographic location or interests obtained from a user-provided profile. Not mentioned is the more creepy, big-brotherish possibility that, in the absence of user-supplied information, Google will troll its data cache for the material it has on a dialer and use that to target ads.

There's also something here to potentially annoy advertisers, as well. Although the patent covers the possibility of billing advertisers based on the amount of ad content that users hear, it also reserves the ability to bill if only a tiny snippet plays before the call or hold session is terminated.

It's clear that the patent covers approaches that could seriously annoy pretty much everyone involved in the process, including the call's dialer and recipient, and the advertisers that pay for the service. But it's important to emphasize that patents are generally written far more broadly than the actual implementation, and Google may choose to implement only some of the more problematic practices. Indeed, it's possible that it may skip using this patent in its entirety. The chance to open an entirely new revenue stream, both through its own voice service and via partners among the telcos, will undoubtedly be very tempting, though, and users might well put up with the practice if it means free calling.

Found via Unwired View.