The people with the stolen passports were booked through to Europe. Apparently their tickets were booked by an Iranian businessman who's done lots of business with the agent before. Sounds a lot like a couple of potential illegal immigrants skirting the higher-security airports.
Plenty of people here might know more than me about cellphones, but when a friend of mine died last year, I accidentally called his cell number and got a ring followed by a hangup. Checked with his wife to make sure she had closed that account, and she had not. My guess was that voicemail was full. I do not think he's still alive hiding out in Area 51.
It looks freaky now, but once the wreckage is found (and it will be, eventually), it will seem obvious why the plane is wherever it is. But it might not happen for a few weeks or months, and by that time the conspiracy theorists will have invested too much time and effort to admit it and the rest of the world will have moved on to the latest celebrity scandal.
My gut feeling is a hijack or bomb, but I have only negative evidence to support it.
We're so spoiled by real-time tracking and instant information that we forget that there are areas where it doesn't work, and that a shallow, muddy sea or jungle-covered mountainside can swallow even something as big as an airliner quite effectively. Heard an interview with one of the Vietnamese pilots, and he seemed disappointed but not surprised that they hadn't found anything. He said the sea is bigger than it looks on maps and it's easy to miss things by a few miles, only to be shocked when they turn up where you thought you'd looked.