That depends on type of Ooma system you have and whether or not you’re using it with a basic landline back-up. If you’re using your Ooma system without a landline or if you have an Ooma Telo system, you won’t be able to make or receive calls until the power is restored. With a Premier subscription, you can configure the “Call forward on Internet outage” feature to ring another phone number in case of a power outage. If you’re using the Ooma Hub system with a landline back-up and the power goes out, all the lights on your Ooma devices will turn off and your dialtone will revert to your local landline. With a line-powered phone, you’ll be able to make and receive calls, but you may incur charges from your local phone company. If your phone requires electrical power, you won’t be able to make calls until the power is restored.
Note: The option to connect your Ooma Telo to a landline is no longer available in units that were manufactured after April 2011.