In any case you seem to be mistaking Soviet Union for Mongolia or some other equally well-developed country. Moscow stats - http://mgts.ru/company/about/foundation - 162K new lines in 1970, 89K - in '71, 130K - in '72, etc.
Relevant because the theory talks about an increase in phone lines. To talk about increase you will need to see the progression over time. The soviet union fell apart late 80s early 90s. What's up with the attitude?
For that theory to work there has to have been a point where they could monitor all the phone lines.
Parent poster is making it clear that such a point was well over decades before the soviet union fell, so it's hard for the theory to explain the fall.
That's like saying there need to be a policeman for each citizen. Things don't work like that. The system isn't in one to one relationships.
Anyway it's a theory I heard somewhere I make no claims about it's validity. However I do believe there is something to it which explains why North Korea is so gong ho about controlling information (and being so successful at it)
There is a reason why they weld the radio station to one frequency and why the the US is trying to smuggle radios over the border.
