With telephone service, it's fairly simple. In the US, it wasn't a case of the government looking at AT&T and thinking to themselves: "That looks nice, I want it.". AT&T was granted a legal monopoly on telephone service in exchange for being regulated as a public utility, providing universal lifeline service, and all that. Many other nations followed the US's lead and set up similar telephone monopolies.
In the '80s... during the Reagan administration no less... the US government finally realized how stupid a move that was and broke AT&T up into the "Baby Bells". Unfortunately, the government seems to have regressed to 1900's thinking and has been letting AT&T reassemble itself and to allow the other bandwidth companies to follow suit; leading to the sack of crap that our telecom infrastructure is and the reason that net neutrality is even an issue.
That aside, you're right. It is absolutely ludicrous to suggest regulating Google or Facebook as though they were utilities. Will they be granted similar legally-mandated search engine and social network monopolies in exchange for having their destinies essentially stolen from them? Either way, it's be the death of both companies. AT&T may have had Bell labs turning out some neat technologies. But the pace of innovation and upgrades of their network was appallingly lethargic. Any tech company forced to labor under the same conditions would just die the second the monopoly was broken, and no longer legally-mandated, under a more enlightened administration. (To be fair, that may be these particular regulators' goal.)