You should have surge protection on all of your phone lines, and either a surge protector or a UPS (Un-interruptible Power Supply) with surge protection on the power line.
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.
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 (usually rated for 30 volts) should be used on BOTH ENDS of any circuit going between two buildings.
Remember that watts and "VA" are only the same with a true RMS sine wave. Most small UPS units use a modified square wave, so de-rate the VA to about 80%. In other words, if the UPS says 100 VA, it would be capable of delivering about 80 watts, unless specified otherwise. (from electro-guru Karen Houston)
IMPORTANT: Phone line protectors must be connected to a good ground. This can be done by mating a phone line protector to our AC protector.