Ho hum. Blah. Humbug.
The fact that most if not all handsets were basically at the mercy of whichever strange base station AND that it wasn't all that hard to set up your own rogue base station AND make just about all phones in the vicinity has been known for quite a while. The police (or possibly whichever secret services) did it first, of course, but any person with reasonable technical skill could do it, and it's only become easier with the availability of open base station software.
So this isn't really something new, though easier to obtain and cheaper than previous approaches. As a result, I wouldn't call it "major". We've just had rebels take over an entire country's mobile infrastructure. Now THAT would be MAJOR.
What's much more interesting is that the network will inevitably grow more open and as such we're all walking around with the equivalent of unpatched windows XP on a hostile internet without any firewall, and moreover, the security people know this and nobody is doing anything whatsoever about it. It's not about these rather insignificant femtocell things. It's about the nature of the network.
<wanders off, mumbling about security scares, clueless hacks, and so on, and so forth>
Paris, for shurely she knows what to do with a cellfone.