wait a sec.. what the hub does? it converts your phone calls into voip calls..
what the difference you say? it is very simple. if your power is cut - you cant make the call through your hub..
if you had 'normal' phone however - you could
(unless you exchange had power failure too - which would be really in case of a truly catastrophic event - like a nuclear blast within 100 mi)
please tell me I am wrong