Myth #1: It's OK to use your cell phone in-flight. Not exactly. As I write this, the major carriers still forbid you to use your cell phone on a plane, citing Federal Communication Commission rules. In fact, a 2003 study by the UK Civil Aviation Authority determined standard cell phone use can make a compass freeze or overshoot its actual magnetic bearing. A wireless device can also interfere with an aircraft's navigational equipment. (Other studies have not found such a strong link, leading many passengers to believe the real reason airlines had banned cell phones was to boost profits from their onboard satellite phones.)

Myth #2: Onboard wireless is new. Hardly. People have been communicating wirelessly from the main cabin since there have been wireless devices (never mind those overpriced satellite phones). A few years ago, I reported that the Federal Aviation Administration (FAA) was looking the other way while air travelers were firing up their personal digital assistants (PDAs) in-flight and checking e-mail. I have personally used a cell phone on a plane, and I have flown next to people who have used their cell phones, particularly when they are over a populated area or flying at a lower altitude. What is new is that the FAA appears ready to sanction equipment designed to send and receive wireless signals onboard.

Myth #3: Onboard wireless is cheaper than old satellite phones. Seat-back phones charged $1 a minute or more, and the connection quality was often less than spectacular. No one knows how the new onboard cell phone service will be priced, but you can bet that the airlines and the technology firms that were used to install the onboard cellular receivers will be vigilant in recovering their costs. As it stands, users of onboard cell phones will either be subjected to roaming charges of some kind or they will have to use special equipment to access the special onboard cellular signal. So if you're counting on the new phones being cheaper than the old ones, don't.

Myth #4: Onboard wireless means your cell phone works on the plane. Not even close. It doesn't even mean anything on the plane is wireless-enabled. Consult your airline's Web site carefully before making plans to connect wirelessly. For example, KLM just began offering text messaging and e-mail on its Boeing 777s, which operate on routes to New York, San Francisco, Sao Paulo, Cape Town, Dubai, Tokyo, Shanghai, Beijing and Manila. A cursory glance at the service might lead you to believe that you can use your cell phone to send messages. Not true. In KLM's case, you use your in-seat, in-flight-entertainment system to send the messages at a cost of $2.50 each. Other airlines have installed onboard high-speed wireless Internet services, but haven't added the cellular equipment.

Myth #5: An onboard wireless connection means you'll be more productive. This is perhaps the biggest misconception about onboard phones — that somehow we won't be able to live without them (particularly as business travelers). Don't count on it. A plane trip without a phone may actually be the ideal time to focus on that presentation or report, away from the interruptions of a ringing handset. True, cell phones can — and do — make us more productive. But there's a time for everything. And that includes a time to turn off your cell phone.

Understanding that onboard cell phones are a new and quickly evolving technology which may help you decide whether to take your phone on your next flight, or to turn it off and stay disconnected for the duration.

It's your call.