The new app from 02 called "Tu Go"
Not really break through technology but the first of the 4 to offer a service where your call is transferred when your phone doesn't have a phone signal to any internet based device, including the phone. So essential the mobile call gets turned into a Skype like internet based call, you can also do the same with out going calls the minutes come off your tariff (I have unlimited) if you have a long text to send, do it on the laptop or tablet and send it over the Tu Go.
So essentially you could have absolutely no phone signal but receive calls if you can connect to wifi