Hey -- did you hear about the $17,670 iPhone?

No, it's not a gold-plated version designed for Paris Hilton.

It's the one everybody's buying. The one in your local Apple ( AAPL) store.

You may even have bought one ... without realizing it.

That's because, for most Americans, the true cost of Steve Jobs' latest "must-have" product isn't what's on the sticker. It's what they had to plunder from their retirement savings -- if any -- to pay for it.

Do the math ... if you can stand it.

A $599 iPhone comes with a minimum service plan of $60 a month for two years. Outlay: $2,039.

But if it's not a work expense, a customer in, say, the 25% tax bracket actually had to earn $2,720 to pay the bill.

Sound bad? It's even worse.

Take an iPhone customer who's 30 years old and is not maxing out contributions to his or her 401(k) retirement plan (few are).

In that case, the $2,720 could have been invested tax free. Earning a pretty reasonable 5.5% after inflation over the next 35 years, it would have grown to ... $17,670.

You read that right.

In short: That's how much this customer withdrew from retirement savings to pay for an iPhone.

And if he or she used a credit card and takes a year to pay off the debt, the true cost rises above $19,000.

That's some phone!

OK, this is an exercise. The actual numbers will vary from customer to customer, based on cellular plan, age, tax bracket and retirement age.

But it tells a story.

If someone is already rich and has no worries about retirement, this may not matter.

But hardly anyone is.

Bob Glovsky, head of the financial planners' program at Boston University, points out that most Americans are saving far too little for their retirement, if anything at all. "Americans are a nation of consumers, not savers," he says.

Retirement is getting more expensive than ever. People are living a lot longer, and their medical costs are much higher. Meanwhile, our national savings rate has collapsed.

"The younger generation will be the only ones responsible for their own retirement," Glovsky says. "They can't expect anything from Mom and Dad because the boomers didn't even save enough for themselves."

In numbers? The Employee Benefit Research Institute says that among Americans between 25 and 34, less than half have saved more than $10,000. Less than one in three has $25,000.

For those between 35 and 44, the picture should be a lot better. It isn't.

Less than half have more than $25,000.

This isn't really about the iPhone. It's just about shopping ... and the true cost of the things we buy as long as we haven't saved enough for the things we will need.

Everyone understands how savings need time to grow. And most know that the average American is grossly undersaved for retirement.

But when the latest "must-have" consumer item comes along, hardly anyone seems to put two and two together. Instead, they rush out, waving their plastic.

In keeping with TSC's editorial policy, Brett Arends doesn't own or short individual stocks. He also doesn't invest in hedge funds or other private investment partnerships. Arends takes a critical look inside mutual funds and the personal finance industry in a twice-weekly column that ranges from investment advice for the general reader to the industry's latest scoop. Prior to joining TheStreet.com in 2006, he worked for more than two years at the Boston Herald, where he revived the paper's well-known 'On State Street' finance column and was part of a team that won two SABEW awards in 2005. He had previously written for the Daily Telegraph and Daily Mail newspapers in London, the magazine Private Eye, and for Global Agenda, the official magazine of the World Economic Summit in Davos, Switzerland. Arends has also written a book on sports 'futures' betting.