"The laboratory results indicated that the phones not only produce emissions at the operating frequency, but also produce other emissions that fall within airplane communication/navigation frequency bands (automatic direction finder, high frequency, very high frequency [VHF] omni range/locator, and VHF communications and instrument landing system [ILS]). Emissions at the operating frequency were as high as 60 dB over the airplane equipment emission limits, but the other emissions were generally within airplane equipment emission limits. One concern about these other emissions from cell phones is that they may interfere with the operation of an airplane communication or navigation system if the levels are high enough.....see..."http://www.boeing.com/commercial/aeromagazine/aero_10/interfere_textonly.html...and some basic amateur radio stuff re harmonics i first encountered in the 60s which still applies today....
http://www.arrl.org/files/file/Techn...age/Hallas.pdf.