Is your iPhone set to roam?
No. The switch is off, as it's supposed to be.
Not sure. How do you check again?
Yes! And I didn't flick the switch.

Check your smart phone's settings before traveling abroad to avoid possible sky-high charges.

Santa Monica resident Nathan Oventhal had heard the horror stories about people getting slammed with hundreds or thousands of dollars in roaming charges after traveling abroad with a smart phone. He was determined not to let it happen to him.

During a recent trip to Paris, Oventhal used his iPhone only to snap a few pictures. No calls, no Internet, no e-mail.

Nevertheless, he ended up being billed by AT&T to the tune of $550 for accessing 20 megabytes of data, the equivalent of about 10,000 pages of text or 10 high-resolution pictures.

“How on God's green earth did I use 20 megabytes?" an incredulous Oventhal, 64, told me. “All I did was use the camera."

His experience serves as a cautionary tale for all iPhone, BlackBerry and assorted smart-phone users.

Always check the settings of your wireless device before traveling abroad. Even if you never fiddled with the switches, you may be vulnerable to sky-high roaming charges.

Oventhal's troubles began the second time he tried to use his iPhone camera while sightseeing in France.

He turned on the handset and was greeted with a text message from AT&T warning that his international data usage was “very high."

Spooked, Oventhal immediately switched off his iPhone. He contacted AT&T after returning to Southern California. A service rep said he had run up about $550 in roaming charges while abroad.

Oventhal wanted to know how this could have happened, considering that he never made a call or accessed the Web or his e-mail.

He said the rep explained that Apple routinely sends software updates to iPhone users. What must have happened, the rep said, was that when Oventhal flicked on his phone to use the camera, the update occurred, and voil -- a big, fat data charge.

Oventhal said the rep then helpfully offered to enroll him in a $59.99-a-month data plan, backdate it to the beginning of Oventhal's vacation and thus make the problem go away for a relatively small fee.

“It's like blackmail," Oventhal said. “They tell me I owe more than $500 and then say they can charge me $60 instead. So of course I'll pay it. Who wouldn't?"

Not so fast. First, there's the matter of the purported Apple software update.

“We don't do that over the air," said Natalie Harrison, an Apple Inc. spokeswoman. “If he didn't plug his iPhone into a computer, he didn't get an update."

So why would the AT&T rep say that? Harrison had no clue. Nor did John Britton, an AT&T Inc. spokesman.

Then there's the matter of Oventhal's data-roaming setting. The default setting, according to AT&T and Apple, is off. That is, unless you switch it on, your iPhone won't access the Internet or e-mail while you're overseas.

Oventhal told me he never played with the setting. He didn't even know where to find it until I walked him through the process. Lo and behold, his data-roaming switch was in the “on" position.

What likely happened is that as soon as he turned on his iPhone in Paris to use the camera, it started downloading e-mail. There's the 20 megabytes of usage.

But how did the switch get turned on? Oventhal had no explanation.