Several news stories and discussions lately have said that cell phones were an important part of the parcel bombs. BBC News explains exactly why in a story called Yemen parcel bomb ‘was 17 minutes from exploding’

Both bombs were wired to circuit boards from mobile phones but did not contain the SIM cards needed to receive calls, US officials have said. This indicates the phones were to be used as timers.

I hope that helps clarify enough so people will stop saying that wireless networks and cell-coverage on planes are an unacceptable risk. The phones had timers not signals; so we might as well ban clocks and watches from airplanes if we are going to pretend that a technology ban makes us safer.