(FORTUNE Magazine) – "Are you the type of person who's interested in making money?"

You might think anyone over age 12, upon hearing that question from a stranger on the phone, would risk elbow injury hanging up as fast as possible. But apparently not. For this was the opening line that worked best when telemarketers phoned chumps around the country to bilk them out of thousands of dollars--sometimes hundreds of thousands--for an investment scam run by one Eric S. Stein. It worked great. Stein, operating out of Las Vegas, separated 1,750 investors from $50 million in the largest investment con in Nevada history, which is saying something. Eventually someone he owed money threatened to tell law enforcement if Stein didn't pay. Stein thought the guy was bluffing, but he wasn't. So now Stein is sitting in a federal prison in Massachusetts, serving much more time than he had expected in a much worse place than he had imagined, really wishing he hadn't done what he did.

I stopped by to talk with Stein because the issue of prison time for our era's famous white-collar criminals is finally advancing, you might say, from the theoretical to the concrete. Martha Stewart was due to be sentenced in mid-July, after which the Bureau of Prisons will announce where she'll do the time. Her friend Sam Waksal has spent nine months at a prison camp in Pennsylvania; he has just over five years left. Lea Fastow, wife of former Enron CFO Andrew Fastow, asked to serve her one-year sentence at a minimum-security camp like Waksal's but instead was scheduled for a mid-July check-in at the Federal Detention Center in Houston, where she'll spend her days alongside various killers, crack dealers, and thugs. Her husband is facing ten years, location not yet announced, though sentences of that length are usually served in the big house, not a minimum-security camp. Frank Quattrone is scheduled for sentencing in September.

Eric Stein, 45, is not among that crop of celebrity business convicts. He ran his scam in the mid-1990s, asking investors to send money he'd supposedly use to run direct-response TV commercials selling items like a Christmas tree fire alarm ("It worked, but in a real fire it melted after a few seconds," he says) and a pet vacuum ("It just made the dog feel good, but that was fine because he smiled in the commercial"). Minimum investment was $5,000, and investors were promised a 50% return in 90 days. Incredibly, lots of them bit. Of course Stein ran hardly any commercials. Mostly he just kept the money, which poured in at an astonishing rate--$1 million a week, sometimes $1 million a day.

He knew he might get caught, but he figured he was managing the risk. "We were always doing calculations. We had lawyers--they'd been disbarred, but they were still lawyers--giving us cutoff points for dollar amounts." Stein and his associates thought if they limited the size of the fraud, then any eventual prison sentence would be minimal, and they'd serve their time at some Club Fed prison, "someplace elegant where we'd play golf and go swimming." But they were mistaken.

Instead of a wrist slap, Stein got an eight-year sentence and soon learned Club Fed no longer exists. Those federal prison camps--most famous were the Eglin camp in Florida and Allentown in Pennsylvania--have been tightened up since the '80s. Stein now lives at the Devens camp near Ayer, Mass. These places are not nice, though they're nicer than the razor-wire-and-gun-towers prison where Stein lived until about a year ago, with assorted rapists and pedophiles, and a whole lot nicer than the Nevada county jails where he spent three years while his case got resolved and where one cellmate, he says, was a double murderer.

Whether this is any more or less than today's corporate crooks deserve is a question for another time. But the grim reality of prison life for today's white-collar criminal--the utter absence of privacy, the body-cavity strip searches, standing in line 90 minutes, much of it outdoors in any weather, to get unspeakable food--is definitely worse than they or the public expect. Not long before Stein and I talked, former Rite Aid CEO Martin Grass accepted a plea deal that could send him to federal prison for up to ten years. Stein's reaction: "Guaranteed, this guy has no clue of what awaits him."

Stein's message to the outside world is simple: "If you are considering committing a financial crime, do not do it." He thought he understood the tradeoff, but he didn't. He wishes more people did.

Oh, and if someone calls and asks whether you're the type of person who's interested in making money? That's also simple: "Just hang up!"

GEOFFREY COLVIN, senior editor at large of FORTUNE, can be reached at gcolvin@fortunemail.com. Watch him on Wall $treet Week With FORTUNE, Friday evenings on PBS.