There are actually two rules that cover cell phone usage on airplanes. The FCC rule is 22.295 and states:
"Cellular telephones installed in or carried aboard airplanes, balloons or any other type of aircraft must not be operated while such aircraft are airborne (not touching the ground). When any aircraft leaves the ground, all cellular telephones on board that aircraft must be turned off."
As others have stated, this rule is necessary to avoid problems with a cell phone signal being received by multiple towers and causing interference. This rule has nothing to do with airplane safety.
There is another rule, however, by the FAA which related to portable electronic devices. FAA rule 91.21 states:
"(a) Except as provided in paragraph (b) of this section, no person may operate, nor may any operator or pilot in command of an aircraft allow the operation of, any portable electronic device on any of the following U.S.-registered civil aircraft:
(1) Aircraft operated by a holder of an air carrier operating certificate or an operating certificate; or
(2) Any other aircraft while it is operated under IFR."
(That includes all commercial airlines.)
This rule is intended to avoid problems with electronic devices interfering with the navigation, communication, or other aircraft systems. There are exceptions, however, the most important of which is given in (b)(5) of the same rule:
"(5) Any other portable electronic device that the operator of the aircraft has determined will not cause interference with the navigation or communication system of the aircraft on which it is to be used."
In other words, the operator of the aircraft has the ultimate responsibility for determing which devices you can use.
Now, on to the more important question, can a cell phones cause interference to aircraft systems? Tests have been done which show no interference, but there are too many variables which the tests cannot duplicate. What if a cell phone is not operating properly? What if there is a problem with the airplane that makes it particularly sensitive to interference? Search around the internet and you will find pilot anecdoes about hearing cell phone conversations in the cockpit. There is no system for reporting or tracking these types of interference, so anecdotes are about the best evidence you are going to find. If we accept these anecdotes as fact, then we can say that some cell phones may cause interference with some aircraft.
To be in compliance with the FAA rule, the operator of the aircraft must determinie if a portable electronic device can cause interference with any of the navigation or communication systems on the aircraft. The rule doesn't specifically state whether each individual device must be excepted, or if whole classes of devices may be excepted. For example, cd players are an exception to the rule on most airlines. If we assume that the rule applies to whole classes, and given the above reasoning, then cell phones can cause interference and must not be used. If the rule applies to individual devices, then each cell phone could be tested to see if it causes interference. But that might take a while!
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As others have stated, this rule is necessary to avoid problems with a cell phone signal being received by multiple towers and causing interference. This rule has nothing to do with airplane safety.
There is another rule, however, by the FAA which related to portable electronic devices. FAA rule 91.21 states:
(That includes all commercial airlines.)
This rule is intended to avoid problems with electronic devices interfering with the navigation, communication, or other aircraft systems. There are exceptions, however, the most important of which is given in (b)(5) of the same rule:
In other words, the operator of the aircraft has the ultimate responsibility for determing which devices you can use.
Now, on to the more important question, can a cell phones cause interference to aircraft systems? Tests have been done which show no interference, but there are too many variables which the tests cannot duplicate. What if a cell phone is not operating properly? What if there is a problem with the airplane that makes it particularly sensitive to interference? Search around the internet and you will find pilot anecdoes about hearing cell phone conversations in the cockpit. There is no system for reporting or tracking these types of interference, so anecdotes are about the best evidence you are going to find. If we accept these anecdotes as fact, then we can say that some cell phones may cause interference with some aircraft.
To be in compliance with the FAA rule, the operator of the aircraft must determinie if a portable electronic device can cause interference with any of the navigation or communication systems on the aircraft. The rule doesn't specifically state whether each individual device must be excepted, or if whole classes of devices may be excepted. For example, cd players are an exception to the rule on most airlines. If we assume that the rule applies to whole classes, and given the above reasoning, then cell phones can cause interference and must not be used. If the rule applies to individual devices, then each cell phone could be tested to see if it causes interference. But that might take a while!