They used to use what is called a repeater it would bounce from one tower to another tower repeat the signal and the message and send it on now since the evolution of the Web and the wireless networks there is a whole different system of connectivity in place that is used now. Honestly I believe 911 will work. Your guess is as good as mine if there is any carrier left that will be of use,also there were many privacy issues involved in that communication system. Phone calls could be picked up over a regular police scanner that was in scan mode.