One of the great things about the traditional PSTN is that it keeps working when the power goes out. I’ve repeatedly read others recommending that people sustain traditional POTS service at least in part because of this fact. Their theory being that VOIP service isn’t sustained during a power outage. But this need not be the case given just a little forethought.
Prior to migrating to Asterisk we had been using a Panasonic KX-TG4000 KSU (seen left). This phone system has four FXO interfaces for analog lines.
It also featured a built-in battery backup so our phones stayed up through power outages. In migrating to VOIP within our home and office I felt it necessary to strive for this kind of reliability. It has certainly made my wife happier.