Brands tap growing use of non-voice cell phone applications - I'm going to bet there are two things you make sure you have when you walk out the door: your wallet and your cell phone. Except teenagers who might forget their wallet. In fact, while some of us perceive cellular technology as a mere convenience, for many of us it is indispensable.

This represents an opportunity to communicate with consumers. When I recently posed this to a group of marketing professionals, they were disgusted. But this opportunity is a lot more than hawking ring tones. And if trends in Europe are any indication, it's a marketing opportunity that cannot be ignored.

Here are some cool applications I learned about:

• In Sweden, if you want to park in an open, designated spot, you can reserve it via your cell phone for a certain time period. If you return earlier, you adjust the timeframe. The charge appears on your cellular bill.
• In the U.K., Cadbury runs a sweepstakes using codes on candy wrappers. To see if you've won, you text message the code to a designated number.
• Throughout Europe, if you want to log your opinion or get a coupon, you can do it through your cell phone.

While Americans have lagged in digital adoption, some research indicating a growing opportunity:

• A recent report by Forrester Research shows that Gen Yers use Web-enabled phones for fun—streaming video files, texting friends, sending pictures or playing games—but older generations are much more likely to use theirs for commerce—buying event tickets, checking stock prices or researching planned purchases.
• The Yankee Group calls text messaging the leading source of revenue for wireless providers outside of voice service. My kids would rather text than call.
• EMarketer reports that 76.5 percent of Americans have a cell phone. This will climb to 95 percent by 2010.

Coca-Cola, Fox and Timberland have recently launched successful mobile marketing campaigns. Even Britney Spears promoted her new perfume via cell. The possibilities are endless.

But there are three important caveats:

• First off, to be truly effective, mobile marketing should not stand alone. It has to be part of an integrated marketing mix. That's the way people learn.
• Second, we have to get serious about opt in. The misguided notion of opt out, as supported by the Direct Marketing Association and the U.S. government, just won't cut it here. Mobile marketing isn't for everyone. We need a strict definition of opt in and the marketing community needs to live by it. If this goes the way of the National Do Not Call Registry, which now contains well over half of all U.S. residential phone numbers, we will have killed the golden goose.
• Third, to get customers to opt in—and to stay opted in—marketers have got to provide value. In mobile marketing, the customer is in control.

A friend once told me that at the beginning of the dot-com bubble he had been invited to leave his job and join the crew launching eBay. His reaction was, "An online swap meet? Oh, please." Some feel the same skepticism about mobile marketing.

In Italy, when people answer the phone, they say, "Pronto," which, in the vernacular means, "I'm ready."

Are you?

Scott Hornstein is principal at Hornstein Associates, a direct marketing consultancy in Redding, Conn. Clients include Microsoft, HP, The Phoenician. He is the co-author of Opt-In Marketing: Increase Sales Exponentially with Consensual Marketing (McGraw-Hill, 2004).

Contact: (203) 938-8715; scott@hornsteinassociates.com