(CNN) -- Fighting boredom in the skies is big business.
Panasonic's X-series in-flight entertainment system.
Last year airlines around the world spent about $1.4 billion on in-flight entertainment hardware and more than $400 million on content, according to research firm IMDC.
It's ironic, then, to see their offerings often being ignored by passengers with iPods or other personal entertainment devices. Such passengers carry their own videos, music and games.
But as long as there's a larger screen on the seat-back right in front of them, why not let them use it?
Many stiff-necked iPod users have pondered that question, especially on long flights. "Prison Break" episodes downloaded from iTunes would be so much more enjoyable without having to squint down at them on a tiny screen.
Increasingly, airlines are getting the picture.
Since mid-May passengers flying on Singapore Airlines between Newark and Singapore have been able to link their iPods to the in-flight entertainment systems. Other airlines around the world are lining up similar offerings.
"Supporting passengers' own devices is one way for an airline to enhance their product and gain an advantage," says Robert Smith, a senior market analyst at IMDC.
"Consumers are carrying increasingly powerful devices, and some will want the option of having power, a bigger screen, and somewhere to put their iPod."
Airlines are not alone in adjusting to the new currents. Some hotels now offer special ports so guests can hook up their iPods (or other devices) to the audiovisual equipment in the room.
And some car makers are building USB ports directly into dashboards so drivers or passengers can easily access their MP3s and such while on the road.
But it's in the skies -- or more accurately in cramped metal tubes in the skies -- where the battle against boredom gets particularly desperate, which is why Internet access, cell phone reception and satellite radio are also being offered to entertain passengers.
"Just about every airline we speak with has asked us to demonstrate this feature," says Theresa Yeoh, a spokesperson for Panasonic Avionics.
Her company makes the eX2 in-flight entertainment system used by Singapore Airlines on its Newark-Singapore route.
It works like this: An export jack is built into the airline seat. Passengers plug their iPods or iPhones into this jack to enjoy their content -- videos, music, games, photos -- through the system's seat-back screen and headphones. The eX2 also powers the iPod, so customers can leave the plane with a fully charged device.
There are downsides to such systems, though. The biggest, perhaps, is compatibility. Inevitably, the same kind of compatibility hitches that plague consumers in the tech world are now cropping up in the airline cabin.
For instance on the Singapore-Newark flight, Microsoft's Zune player, and many other personal media devices, will not work with the eX2's export jack.
That's clearly a marketing advantage for Apple (with the airplane becoming a giant iPod accessory in the sky), but passengers with other devices might get annoyed.
Yeoh wouldn't disclose details on the business arrangement with Apple but says that under Apple's "Made for iPod" program, this is the first solution designed specifically for the commercial airline market.
Another problem: there's no privacy on the seat-back screen. That's a worry when some passengers might watch questionable content. For instance a passenger could play airplane disaster videos and be seated next to someone with an intense fear of flying.
Other problematic scenarios pop easily to mind. One potential solution could be in-flight announcements stating an airline's policy regarding appropriate material.
Some of the new possibilities are more promising, such as shopping, for instance. Why not spend your time in the skies cramming new songs, TV shows and audiobooks into your iPod?
"Airlines offering content for download to passenger devices in-flight is very likely in the future," says Smith.
"They can store the content on an onboard server, or offer downloads as part of an onboard broadband Internet service. The constraint is no longer the technology but one of legal rights management."