This is not just a COSMOTE issue but within an EU directive about providing VOIP services**. If you wish to find out if your land line will work during a power cut, please ring Cosmote customer services 13888 (They have a very good service in English) Remember, ONLY option (1 ) below will definitely work during a power cut and many of thes lines are being switched to (3) which will NOT work.
Below is an extract from an Ofcom guide - note than land lines with cordless phones will NOT work anyway
Many of us experience power cuts from time to time, which can be caused by bad weather or problems with electricity lines. The first things we look to lay our hands on are likely to be the emergency torches or candles. But what if you need to make a phone call - to check on relatives, to report the power cut or even to contact the emergency services in the event of an accident or fire?
You should still be able to use a traditional plug-in landline phone during a power cut as long as nothing has happened to bring the phone network down, too. This is because your telephone line takes its power from the local telephone exchange, which has back-up power available.Cordless landline telephones are very unlikely to work in a power cut, even if they're fully charged. more.....
Resilience in the event of a power cut
|1 Corded phone||Likely to work as it gets its power directly from the exchange.|
|2 Cordless phone||Will not work as the unit that plugs into the phone socket (the base station) also needs mains power to operate and doesn't tend to have a battery.|
|3 Voice over IP phone or other fixed broadband-based communications service||Will not work as the broadband router, and potentially other equipment in the home, needs mains power to operate and doesn't tend to have a battery.|
|4 Mobile phone||May work providing it is charged, and 'active', depending on how widespread and long the power cut is.|
**OTE provides reliable and qualitative communication to all people in Greece, even in the most remote and inaccessible areas of the country, utilizing more than 35.000 km of optical fibers, numerous satellite, underwater and terrestrial international links. Ιnfrastructure is also continuously upgraded, following the technological developments. The telephony network will be replaced by VoIP/IMS (IP-Multimedia-Subsystem) architecture. TDM digital exchanges, are gradually withdrawn, in order to be replaced by the modern All-IP network architecture within the following years.
This is not just a European concern. For more on the issue see links below
N Zealand Broiadband:What happens to the phone & internet services during a power cut?
Regulatory Implications of VoIP (option 3 above)