I’ve been paying my bills with iPhones. Not with apps or on bank sites—I’ve been using the Apple (AAPL) hardware as currency.

It started by accident in December, during a business trip to New York. I live in Rome, where domestic work comes cheap and technology is expensive. An unlocked, gold, 32-gigabyte iPhone 5s that costs about $815 with tax in the U.S. goes for €839 (about $1,130) in Italy, roughly a month’s wages for workers who do laundry, pick up kids from school, or provide care for the elderly. When one worker heard I was visiting the States, she asked me to pick her up an iPhone in lieu of the equivalent cash for work she’d done. Lining up inside the Apple Store on Fifth Avenue, I was surrounded by shoppers speaking languages from around the world. The salesman looked stunned when I said I wanted an unlocked iPhone. Just one?

A new shipment of unlocked 5s phones had just come in, he said, adding that the gold model I asked for was the most popular in Europe and the easiest to resell. To my right, a man with a credit card from a Saudi bank was trying to buy his third and fourth phones of the day. “Make it two,” I said. There was one more step: The salesman grabbed a landline from behind the counter to connect me with my bank’s antifraud department. Purchases from this store, he said, are red flags.

Do the math, and that’s no surprise. Exiting the store with my plastic Apple shopping bag secured by a rope drawstring, I no longer thought of the phones inside as appliances. They were more like gold bars.

Transnational workers rich and poor have long dealt in an ever-evolving system of arbitrage for luxury goods carrying significant price differences around the world. A few years ago, it was Louis Vuitton (MC:FP) andGucci (KER:FP) handbags, bought in Paris by Asians who paid for trips home by selling the purses at a markup. In the early 1990s, Levi’s jeans served a similar function for Americans in Eastern Europe. Today, it’s the iPhone, especially that gold 5s.

Kyle Wiens, chief executive officer of the iPhone spare-parts distributor IFixit, was scuba diving during a break from a November conference in Cabo San Lucas, Mexico, when the dive leader offered free boat trips if Wiens ever returned to Mexico with iPhones to sell at the U.S. price. (The phone costs about 16 percent more in Mexico than in the U.S.) Wiens says he’s seeing more and more widespread iPhone arbitrage. When he goes to China to meet suppliers, he brings a couple iPhones and iPads to sell at cost, as a gesture of goodwill.

Alexander Peterc, an analyst with Exane BNP Paribas whose office sits above the Apple Store on London’s Regent Street, says that for more than a month after the 5s came out last year, people from countries where it wasn’t yet available lined up every day. “They can probably pay their plane ticket by buying two phones and selling them in India,” says Peterc.

Apple CEO Tim Cook has hinted that the cross-border movement of iPhones is important to his bottom line. In July, when Apple reported revenue in Greater China had dropped 14 percent in the previous quarter, to $4.6 billion, he blamed a downturn in purchases in Hong Kong, where tourists and resellers are major customers. Apple spokeswoman Teresa Brewer declined to comment.

$707.41

Average price in the U.S. of a gold iPhone 5S with 16GB of memory, according to Mobile Unlocked

According to a list of iPhone prices in 48 countries compiled by Stanmere (U.K.)-based Mobile Unlocked, the cheapest 5s with 16GB of memory can be purchased for about $700 in the U.S. The most expensive country in which to purchase the same phone is Brazil, at $1,200. At a little less than $1,000, Italy ranked seventh-most expensive, tied with Malta.

Within a couple days of my return, I exchanged both phones for domestic work, valuing them at the $815 I’d paid. The second phone’s recipient sold hers for its local value ($1,130) to an acquaintance, she said, with payments to be made over time. She told me the new owner sold the phone at an additional markup on an installment plan that will cost the final buyer about $1,350.

On a trip to Los Angeles a few weeks after my Fifth Avenue purchases, I found myself in front of another Apple Store. Walking in felt like a visit to an ATM. I asked the salesperson for an unlocked iPhone 5s. The response: Just one?

I didn’t have a buyer lined up, so I did buy only one. Still, when I got back to Italy, I exchanged it within a week, for €600 worth of household work from someone whose phone had been stolen on the subway. She’d bought the stolen one on layaway for €1,000, and is still paying it off.

I was relieved to make the deal: An iPhone’s value lasts only until the next product launch. For now, the 5s is holding steady, even against that other new currency—Bitcoin.