Some years ago, terrorists attacked the London public transport system.
As a consequence there was no effective cellphone service over most of London.
Power was out in places, but only very close to the explosions, there was no general or widespread outage. (I suspect either blast damage to utility equipment, or local flooding from water pipes broken by the blast)
This put my then employers to substantial inconvienience as their business was spread over a number of buildings and heavily reliant on messengers with cellphones.
Many staff were distressed at not being able to contact friends , workmates or relatives.
It was most fortunate that I had about a mile of telephone cable by means of which land line phones could be used externally, simply throw the cable out of the window.
This was mainly for use of staff, but several police officers asked to use the phone, as the police radio system was overloaded.
Walkie talkies worked fine, but we only had 6, and only had means of charging them at one building.
When the immediate emergency was over, I extended my phone line into the local pub, in order to stay in touch as there was still no cellphone service.