Telephones for traditional residential analog service, such as the one provided by Bell, are usually connected directly to the telephone company phone lines which provide direct current to power most basic analog handsets independently of locally available power.
IP Phones and VoIP telephone adapters (also known as ATA, for Analog Telephone Adapter) connect to routers or cable modems which typically depend on the availability of mains electricity or locally generated power. It’s recommended that in your VoIP setup & equipment (e.g., cable modems) you plan to have battery-backed power supplies to assure uninterrupted service for up to several hours in case of local power failures. This way it allows your VoIP Home Phone alternative to Bell and/or Rogers work just as well and for as long as their service. For suggestions or how a battery backup would look like please check VoIP in the Residential market – is really an inexpensive (around $50) plug & play protection that is more than worth it.
Nowadays most VoIP service providers implement services to route calls to other telephone services of the subscriber, such a cellular phone, in the event that the customer’s network device is inaccessible to terminate the call. Also there’s the follow-me feature that allows to send voicemails to email; in which case should there be a prolonged power outage callers will go to voicemail and an email with the message will be delivered. When that is paired with a smart phone email capabilities it allows to retrieve messages anywhere and at anytime.
Shall be noted though the susceptibility of phone service to power failures is a common problem even with traditional analog service in areas where many customers purchase modern telephone units that operate with wireless handsets to a base station, or that have other modern phone features, such as built-in voicemail or phone book features.