If the power outage was widespread, there is also the possibility that the cellular network was in some overload with all of the 'help' calls being made, and that it disabled 3G data as a defensive measure to preserve it's own bandwidth.
Up until a few years ago that scenario would have been unlikely as not many people would actually have noticed, or even cared about, an power cut at 5:30am in August. But recently British Gas, in order to line the pockets of senior management save the planet , have been rolling out smart meters that, among other duties I understand, use the mobile phone network to 'phone home' when problems arise.
In the almost unthinkable circumstance that that that pillar of society, British Gas, may not have thought this through, I wonder if it might result in network overload whenever a power outage arises?