Losing power can cause your Internet connection to go down. If this happens you will not be able to make calls unless you are equipped with a backup UPS, which could power the connection for a limited short duration. Using a UPS to power your modem and VoIP ATA should allow an Internet connection to be maintained for a short duration and should suffice for short local outages, providing that your ISP is still powered up from your connection to their head end. For larger outages the loss of Internet may be more problematic, as for instance a cable company depends on amplifiers to power some of their equipment. If those amplifiers lose power then their system will go down in that area, including both TV and Internet.