Americans take their mobile phones everywhere—many even sleep with their cellphone. That makes the mobile device an ideal way for marketers to reach interested consumers with well-timed alerts.

A survey conducted by Harris Interactive for 1020 Placecast found that 42% of 18-to-34-year-olds and 33% of 35-to-44-year-olds are at least somewhat interested in receiving opt-in mobile alerts from their favorite places.

Among respondents who would opt in to location-based alerts on their mobile phones, more than one-half were interested in messages from restaurants, followed by movie and event tickets, weather, and clearance sales.

Placecast also found that about 90% of consumers have made impulse purchases while out shopping because of a sale, and 22% of mobile users did so weekly. Marketers that let consumers know about local offers at the right place and time might take advantage of such behaviors.

“It’s that unique combination of place and time, combined with a consumer opting in to follow a brand that they care about, that we think delivers an opportunity for relevant marketing,” 1020 Placecast CEO Alistair Goodman told eMarketer. He stressed that such mobile alerts were “marketing as a service, not marketing as an intrusion.”

Connecting people with brick-and-mortar stores they already care about, while they are out shopping and ready to make a purchase, makes mobile marketing a natural way to drive consumers into local stores, 1020 Placecast suggests.

Borrell Associates estimates that local will make up only 20% of mobile ad spending in 2010, or just over $500 million.

“Still, mobile is a category worth watching as the audience grows and as couponing, mobile directory advertising and sponsored text messages find viable applications for local marketers,” according to the company’s “2010 Outlook: Local Interactive Advertising” report.

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Check out today’s other article, “Factors Behind eMarketer’s Revised Online Ad Forecast.”