Depending on where you are the phone service isn't all that reliable. I've reported both phone and power outages via the internet with my laptop and cable modem running from battery and apparently the other end on battery as well. Were in an area which used to be Ameritech, then SBC then AT&T and my phone lines are dead more than they work. We use our cell phones for most calls anymore.
I stick with Verizon cellular, even though they are more expensive they work in more places than anyone else and I always buy a tri mode phone which means it can do analog and have fallen back on analog calls more than once.