SENDING A TEXT MESSAGE

in support of your favorite houseguest on "Big Brother 8"? That'll be $4.14, please 15 cents for the text message and $3.99 per month for the news alert subscription it automatically signs you up for.

Increasingly, fine print means companies don't always need you to enter billing information to begin the start of a long and profitable (for them, at least) business relationship. All it takes is a single click of the mouse or tap of your cellphone keys the equivalent of an electronic signature. "There's usually a 'By completing this action, you're bound by and agree to the terms of this contract,' clause," says Edgar Dworsky, editor for consumer advocate Mouse Print.

Scarier yet, you may never receive an invoice. More fine print enables the company to access your credit card information through a third party, say, your cellphone provider or a partner site with which you do business. Clicking through a Fandango link for a $10 coupon from Reservation Rewards, for example, authorizes the company to obtain your billing information from the movie tickets site. (The post-free trial cost: $10 a month.)

It always pays to read the fine print, but there are other warning signs that you've opted in for more than you wanted. Watch out for these three sneaky ways companies entice you to opt in for expensive add-ons and subscriptions:

1. Uncheck That Box

"It irritates me no end when you're buying something and the company has the little boxes checked already," says Linda Sherry, a spokeswoman for

. Sure, most of the time you're inadvertently opting in to receive spam (a.k.a. marketing offers) from third-party companies, but sometimes it's a bit more painful for your wallet. Buy a computer from Dell, and you're automatically signed up for a free six-month AOL or Earthlink dial-up connection. Thereafter, you'll be charged $9.95 to $12.95 per month.

Travel vendors are particularly notorious for automatic opt-ins, says Ed Perkins, a contributing editor for travel site SmarterTravel.com. Buy a ticket through Spirit Airlines, for example, and you'll find two extras added to your bill: Membership to the airline's Fare Club ($9 for a three-month trial), and basic travel insurance ($12 and up, depending on your fare). "An awful lot of products these sites sell are fully or heavily nonrefundable," says Perkins. "They're hoping there will be less of a hassle with consumers if you have travel insurance." Wanted or not.

Solution: Companies prefill options to suit their needs, not yours, says Sherry. Before you click to confirm a purchase, go through each additional offer to ensure the only boxes checked are the ones you selected yourself.

2. Watch Out for "Free" Trials

In late 2005, the Federal Trade Commission filed lawsuits against ConsumerInfo.com and Freecreditreport.com, charging that the two had tricked consumers into signing up for pricey credit monitoring services ($79.95 per month) in exchange for a glimpse at their credit report. "It's a classic," says Dworsky. "You think you're getting one thing, but you're really signing up for a free trial." And it still goes on today: After purchasing tickets through Ticketmaster, a discount offer on your next purchase pops up. Click through to sister discount site Entertainment.com, and you may get that coupon for the price of a $9 monthly subscription after its three-month free trial expires.

Solution: Be wary of freebies that pop up after a purchase, or are connected in any way to a company that may already have your credit card information. "You're not getting something for nothing," says Dworsky.

3. Beware the $15 Text Message

The pitches are enticing: Trade in your blah ringtone for the catchy beat of Amy Winehouse's "Rehab." But squint a little closer at the fine print on your flashing TV set, and you'll spot a catch. In the case of that ringtone, you'd pay $1.99 through Verizon Wireless and $15 or more per month thereafter through the automatic subscription to its V-Cast download service.

Blame your mother for warning you not to sit too close to the set, jokes Michael Gartenberg, research director for Jupiter Research. Masking the problem further, these charges show up on your cellphone bill rather than your monthly credit-card statement, he says. They're harder to spot there amid the mass of cellphone fees already tacked on to your basic plan.

Solution: Because third-party companies bill you indirectly by tacking charges onto your cellphone bill, the Mobile Marketing Association requires them to use a double-opt-in system i.e., you must request the service and then confirm your interest. That's a red alert you've bargained for more than a one-time purchase. Ringtones.com, for example, requires online entry of a PIN texted to your phone to download a ringtone, while most cellphone providers request confirmation before permitting a text message to celebrity gossip show "The Insider" (which incurs a 49-cent premium content charge).

If you don't confirm, or actively decline, you won't be charged. Just don't expect to get whatever cellphone bling lured you to the site in the first place.