Internet search giant Google may seek to ring-up profits by replacing the standard ring tone most callers hear with paid advertisements.

While some mobile phone users customize their phones so callers hear music rather than a ringing sound while waiting for a person to pick up the phone, most do not.

Now companies are looking to make money off that "dead air" by replacing the ring with paid advertising.

Ring-back ads are a novel idea in the U.S., but they have been popular internationally since debuting in 2008.

Turkcell's Tone & Win, or TonlaKazan, which launched in 2008, had ad campaigns with 50 different brands including Coca-Cola (KO), Unilever (UL) and Kraft (KFT) as well as local companies by 2009.

In return for listening to the ads, callers got up to 40 free call time minutes.

In India OnMobile also launched an advertising ring-back service in 2008.

In 2011, Ericsson (ERIC) reported it would offer a ring-back ad service and in return mobile users would get free product samples, free voice minutes and free online games.