That data includes engine to satellite handshake, and military radar.
A lot of effort and time was wasted searching in the wrong place, even though the lack of wreckage beneath the last transponder location was an immediate sign that something might be unusual about this case. Meanwhile, possible evidence, such as floating wreckage in the Indian Ocean, was being lost.
Also, I would not be surprised if they knew even more than we know now and are keeping it classified because of the possible terrorist element. If the plane is sitting around somewhere, you don't want them to know you know where it is first from watching it on CNN.
Can't say I blame them as the majority of people on board were Chinese nationals.
EDIT: just to clarify -- I'm thinking of how tracking the precise location of a plane at all times is a problem that it seems like we should have a handle on by now, although not necessarily using cell phone technology. (I wasn't thinking clearly about the cell phone signals in this context, though, as people have been correct to point out.)
Cellphone tower records should provide more evidence, because there are sure to be some phones that were not in airplane mode.
Cellphones won't have enough power to connect more than about 50 km from the coast.
And who said there are?
If you read the story, you will see that the plane flew back across land. If you look at a map, you'll see there's no other way it could get to the Indian Ocean
This is a coverage map for one of 4 Malaysian mobile operators.