By now, most people are savvy about scams that involve giving out personal information on the Internet. They know that identity thieves may be lurking behind ostensibly free offers, fake websites and phony e-mails.

But with cell phones people are less cautious. They think they've lost nothing if they give out one of their biggest secrets, their cell phone numbers, in order to play an online game on, say, Facebook. But they may be losing money - because by failing to read the fine print they may be signing up for a "Premium SMS" service.

SMS stands for short message service, better known as text messaging. A premium service may charge a fee - on your cell phone bill - in addition to your cell plan.

Readers complain that the sign-up process for some games is confusing, and that it's easy to sign up for a $10 a month premium service without realizing it.

Some readers have complained about a game offered through SoLow.com; by texting the right number players can win prizes. But to sign up-or even to play the game for "free" - players must disclose their cell phone numbers. SoLow promises not to charge for free games.

Experts say SoLow appears to play by the rules of online marketing - it requires the user to "opt in" twice, and users can cancel the service by texting the word "stop" to "23687." But those who have been surprised to get a $10 a month charge for SoLow say they didn't understand that they were opting in and didn't know how to stop the service once it started.

The company that runs SoLow, SendMe Inc. of San Francisco, said it will give refunds to consumers who feel they were misled. Call customer support at 877-373-6363.

SoLow is available through several cell phone companies, including Verizon Wireless, Sprint, AT&T and T-Mobile. Because readers who contacted me had used Verizon, I asked the firm about Premium SMS providers.

"We advise customers to be aware to whom or to what they are providing their mobile number," said spokeswoman Karen Smith. "We do support Premium SMS campaigns but work to ensure they comply with all mobile marketing guidelines (double opt-in, ability to stop/cancel at any time). If we discover a company is not complying with these guidelines, we reach out and try to resolve the issue. Customers' refunds are considered on a case-by-case basis, often providing credits where appropriate. But we also offer the ability to block - for free - premium messaging."

But blocking may not be practical for corporate cell phone users.

So it's important to be as security-conscious with your cell phone as you are with your computer.

Steve Alexander covers technology for the Minneapolis Star Tribune. Readers may write to him at Tech Q&A, 425 Portland Ave. S., Minneapolis, Minn. 55488-0002; e-mail: steve.j.alexander@gmail.com. Please include a full name, city and phone number.

(c) 2009, Star Tribune (Minneapolis)

Distributed by McClatchy-Tribune Information Services.