bttt
Turning off the cell phone towers is probably going to be too late. How many phone calls could be made (e.g. by computer) in 10 minutes? Lots. The horse will have left the barn.
A complementary tactic is for the cellphone companies to block massive activation of pre-paid cellphones within a short time window. I get lots of calls that go into voicemail when my cellphone is unengaged because the carrier is at capacity and does not want to connect the call. Surely the carriers can detect centrally which phones are pre-paid, and surely they have enough usage data to know what constitutes an aberrant pattern of activation. So they block the calls when the aberrancy is high. A few of the phones may detonate, but 500 would not...