LIKE many flights, the use of mobile phones on aircraft has been subject to unexpected delays. But some passengers, at least, are now sending text messages and e-mails, and soon an Air France plane will go further. Once it has reached its cruising altitude, its “fasten seatbelt” sign will be switched off—and so will a new “no phones” light alongside it. Passengers will then be able to switch on their handsets and make and receive calls.

Airlines are unsure what passengers will make of this. Surveys have found that many people are vehemently against the idea, but others say they would welcome the opportunity to text, access the internet or make calls. So airlines plan to test the market before deciding how and when to allow phones to be used in the air.

This week JetBlue, a low-cost carrier based in New York, launched a free but limited Wi-Fi data service on one of its Airbus A320 aircraft, in partnership with Yahoo!, an internet giant, and Research in Motion, the maker of the BlackBerry. Passengers using Wi-Fi-enabled laptops can use Yahoo!'s mail and instant-messaging services; those with Wi-Fi-capable BlackBerrys can get their e-mail. (The system uses a national network of special ground stations to provide connectivity.) There is no support for voice calls, following the Federal Communications Commission's decision in March that the in-flight use of mobile phones would not be permitted.

But in other parts of the world, voice calling will be allowed. Air France's test will begin on an Airbus A318 in the next few weeks. Rather than Wi-Fi, it relies on a tiny mobile-phone base-station installed on the plane. At first it will allow only mobile-data access and text messaging, but after three months the voice service will be switched on, too. “We will give a questionnaire to every passenger to see what they think before we make a decision to equip more aircraft,” says Marina Tymen of Air France. “If people say they want data but no calls, that will not be a problem.”

Data could prove to be popular because it is less intrusive than voice calls. Qantas, Australia's flag carrier, has quietly been trying out a data-only service on one of its Boeing 767s. Since it was installed in April, some 19,000 passengers have used mobile devices for texting and e-mails, says AeroMobile, the British firm that supplied the system. More airlines will join in during 2008. AeroMobile is fitting out an Emirates aircraft for data and voice. Ryanair's aircraft are being kitted out by OnAir, a rival technology provider that supplied the Air France system and is backed by Airbus. As Europe's pushiest low-cost carrier, Ryanair thinks passengers on its short, busy flights will not mind texting and calls, because the money it raises will help keep fares low (callers will be billed at international roaming rates, with airlines taking a cut). It plans to equip all 150 of its aircraft.

Passengers will still have to keep their phones switched off during take-off and landing. This is to reduce the risk of interference with aircraft instruments—though the main reason why the use of mobiles has hitherto been banned on aircraft is, in fact, to avoid disruption of networks on the ground as lots of handsets pass overhead at high speed. New systems get around this problem by blocking out ground-based signals within the aircraft, so that phones connect to the on-board “picocell” instead. This is then linked by satellite to ground-based networks.

Satellite links have the advantage that they will work even over oceans. The equipment is also much lighter and cheaper than an elaborate earlier generation of satellite technology, which provided Wi-Fi access on some aircraft, but was never widely adopted. Now that the technology works, it is up to passengers and airlines to decide the rules governing its use. Will data prove most popular, with voice access limited to short-haul flights and brief periods at the start and end of long-haul flights? You make the call.