And how on Earth would you know the routing? And how would you detonate it?
If you have the technology to make lead azide and PETN, then surely you would use a GPS or barometric device. Not a mobile phone circuit.
I'm still struggling to see the logic in this.
In this particular case they should have known that UPS would be flying the package/s from Dubai to Cologne. Armed with the phone number of the sim card and an air band radio, a member of an AQ cell in Germany could detonate the bomb from a car parked in a strategic position near the airport as the aircraft approached. Not knowing exactly which flight a bomb was on it might have taken several visits before the correct aircraft arrives. Same scenario in the US of A.
This is all conjecture of course.