Astound phone is a Voice over IP (VoIP) service delivered over your Astound internet connection and requires power to work. In the event of a power outage, your Astound phone service, including 911, will be interrupted unless you have an Uninterruptable Power Supply (UPS) in place.
You can purchase a UPS from sources like Amazon.com. For eight hours of back-up, you would need a robust UPS unit with additional battery back-up like this example. There are also many other more cost-effective options that offer less back up time like this example.
NOTE: cordless phones, or other powered electronics plugged into the phone line, also need power to function.