Looking at the source code of the OS does not change anything, as you don't know which compiler was used or even if the same source was indeed compiled. Even further, if you compile it yourself you still don't know since at this stage you clearly wouldn't trust even your compiler.
I think you guys are getting lost in the hypothetical vs the reality. Is it hypothetically possible, yes. Is there any evidence it is true, no. See my comment below to see how cnet confused a physical bug with some inherent bugging capability of the phone.
Even in the hypothetical, don't you think someone would have identified the "bug" by now? It would need to draw power while the phone is off, that would be measurable. It would need software on the phone. Even without the source code, the bug could be found in the OS or firmware. Do you think the FBI is working with ever phone manufacturer to install this and no one ever leaked that info? There isn't one piece of evidence that it is actually true.
