With a fresh wave of Google Voice invitations going out in the past week, it's no surprise to see media attention turn to the search giant's attempt to move into the mainstream voice-calling market.

However, we hadn't expected to come across a US patent application for a technology that will insert audio advertising into calls made using the new phone service.

Ads tailored to users

The 'Ringback Advertising' application describes three scenarios where ads might be served up - when a call is on hold, when call waiting comes into play and even when the caller is still dialing.

Depending on the parties on either end of the phone, different advertising will be played, suggesting something as targeted as the text ads in Gmail.

New markets

In spite of the huge profits Google is regularly booking through its traditional advertising channels, it's clearly in the company's DNA to seek out new areas to target.

Still, even if Google Voice calls are free it will be quite the feat if users can be persuaded to listen to recorded advertising during a phone call.

As one commenter on the Ars Technica website put it, "That music on hold doesn't seem so bad now."

Via Ars Technica