Even if the frequencies for communication weren't disrupted because of the sudden change after the apocalypse began, they probably still couldn't use their phones after a week if there's no one to maintain the cell towers for communication, especially after most of the electric lines were disrupted.
"Yes, that's why we brought a lot of additional lithium batteries that have a longer lifespan and also additional solar panels if the cell towers are still lacking any of them.
Most of the cell towers in our country already have a lot of solar panels and lithium batteries; we are just going to add some if needed.
Since we need to conserve a lot of power, they're just going to put the tower into sleeping mode after modifying and inputting the frequencies it would receive.
Afterwards, we have to warn all those bases that the communication is only for emergencies as well as important updates.
