The digital phone services used by millions of consumers today are likely to quit when the lights go out, as homeowners found to their dismay in the aftermath of Superstorm Sandy last fall. These services, which use a technology called VoIP (voice over Internet protocol), rely on a modem to send phone traffic over the Internet, and that modem needs power. A backup battery can keep the modem and a corded phone operational during a blackout, but don't assume your telecom provider has included one with the modem they provide.
In fact, that's less likely than ever, according to Consumer World [PDF]. The Boston-based public service group said Comcast recently stopped providing a free battery for its phone modems and now charges $35 if a consumer requests one. Other cable companies, including Cablevision's Optimum service, also charge for a battery, in its case $30. And most cable companies, as well as AT&T U-Verse and Verizon FiOS, charge about $35 or so for a replacement when a battery fails, according to Consumer World.
Check to see whether your modem has a battery backup, and if it does, make sure it still works. If you don't have backup power, contact your phone provider to request one, or look online for a compatible third-party battery. Of course, you might be able to use your cell phone if your home phone is out of commission, but only if it's charged up and the cell towers in your area are operational.