[Centurion2000]

One report said they were putting the body of the phone in one box, the battery in another.

That would prevent someone from accidentally dialing into it until it was ready to be a detonator. That would also allow for a few 'mistakes' to be made from people calling old recycled phone numbers.

[ArmstedFragg]

That would prevent someone from accidentally dialing into it until it was ready to be a detonator

You can't dial into it anyway if it's not activated, or on. I get this picture of some terrorist attempting to trigger an IED and a voice on the phone is saying, "press one to activate this phone, press two, to add air-time....."