Also fundamentally you can look at it like this: If I (as a nation-state) had the ability to embed a kill switch embedded into the telecoms hardware on which other nations depend, and over which I had exclusive knowledge and control, would it be in my interests to do that? Of course it would. Irrespective of which nation state we're talking about that's a Good Idea.

Also, technically such a backdoor capability is almost undetectable (down to a sub-microcode analysis level), as per the Ken Thompson compiler hack.