I’m left rather confused by this local news story. AFAIU a family has been billed thousands of Dollars for roaming data use despite their claim that the iPhone was always in airplane mode. T-Mobile’s response seems to indicate that despite the iPhone’s AP mode being on, data can still be transmitted over the cellular network. Is that really true? I thought AP mode was supposed to shut cellular radios off.
It’s a poor article. If the family turned on Airplane mode via the control panel, it may not stay on permanently (a lot of settings there turn back on at 8 the next morning). You have to go into Settings to turn it on permanently.
So it’s possible the family had a few times with Airplane mode off, despite their not intending that.
Or they turned if off just for a moment to check something and a bunch of other stuff downloaded. I did that in while in Canada a few years ago – I needed a quick Apple Maps update and turned roaming off for 30 seconds. My phone downloaded my email and a bunch of other updates and it cost me $15 in charges.
I always turn off cellular data in Settings when I roam to a country I have no plan for. I don’t think Airplane mode was designed to avoid roaming charges on an ongoing basis.
I travel internationally. Heck, I travel internationally with T-Mobile. T-Mobile’s One plan allows unlimited 2G downloads from most of the world without charge. I checked and Vietnam is one of the countries covered, so I can’t see it happening there.
I do know that if a country isn’t covered by the plan, the rates are set by the country’s carrier. I’ve seen rates as high as $25 per ***mega***byte. It doesn’t take long at that rate to rack up big bills. A single picture can cost you almost $10 to download. In those countries, I turn off background processing and turn
Cellular->Cellular Data->Data Roaming to off. These settings won’t get reset when you turn the phone off or the next day.
Many people also get a local SIM in countries they visit. It’s way cheaper than roaming.