If this is interfering with telephone systems, it may be possible to plug in plain-jane phones directly into the jacks to keep the lines open...unless the phone lines are down, too... Try to keep the main number into the office operational...
Fortunatly cell phones are so ubiquitous that phones are probably not a problem. I don't think it's a problem to get landline phone numbers patched into a cell phone number. The big problem I would assume is the lack of computers. Hopefully they have laptops running on battery power.