iPhone apps, like any mobile phone apps, can be hit or miss. But the March Madness app on the iPhone has turned out to be a slam-dunk for CBS TV advertisers.

Advertisers like Coke didn’t buy in for the mobile app advertising. Instead, all the advertisers for CBS broadcasts of the NCAA tournements got a special mobile bonus – their ads are also showing up in games viewed on iPhones. That app costs users $4.99 to download, and for CBS it is the first stand-alone option for mobile users.

“It’s an innovative iPhone application that gives us an additional way to connect Coke Zero with NCAA fans,” said Coke spokeswoman Susan Stribling to USA Today.

While the mobile advertising was a free bonus this time around, don’t expect the freebie again in the future. Greater mobile distribution should boost the out-of-home audience numbers CBS can tout for advertisers — and put a price tag on.

“As the audience grows on mobile, we’ll be in a position to start talking to advertisers about the rest of these numbers, and we can finally quantify them,” says Chris Simko, senior vice president of CBS sports sales and marketing. He says it’s not really a free ride even now: “People are paying a premium for our audience on broadcast” TV.