Modern phone systems are generally very reliable, but they can be damaged or destroyed by power surges coming from the electric outlet or a phone line.

Phone system warranties usually don't cover damage from surges, and the loss of of a phone system for even one day can be devastating for a business and extremely inconvenient for a family, so USE PROTECTION. 

• Don't rely on protectors installed by your phone company, and don't think you're fully protected if your phone system is connected to a UPS (un-interruptible power supply).
• UPSes keep your equipment running during a power failure, and protect the equipment from power line surges, but usually don't protect phone circuits. We find much more damage coming from phone lines than from power lines. 
• Protectors should be used on BOTH ENDS of any circuit going between two buildings.

UPS Selection Chart for Panasonic phone systems & voice processors

• To use one UPS for both a phone system and a voice processor, add the VA numbers together
• For a twin-cabinet D1232 system, double the VA figure for one cabinet
• Run time figures are approximate. Systems that have to ring a lot of single-line phones will require more power than systems with most or all "proprietary" system phones.