...advising customers to keep their phone batteries charged...
...is a start. If an outage lasts more than a day, whose phone has the stamina to keep going? Some people I see lug an auxiliary battery pack around with them for normal usage, let alone in emergency.
In an emergency situation, just how do you lock down your phone to receive only emergency communications which don't eat battery life? Would these be phone calls, texts, emails? To my mind the best way to do this is to have a separate phone with separate email address. All normal comms will ask you to manually redial/resubmit to the emergency device.
How do you communicate status out from the disaster-stricken area? A lot of companies use Twitter for this purpose, but what happens when that's down? Perhaps it's time to revisit NNTP.
Biting the hand that feeds IT
