Dunbar's Number and the falling cognitive burden of soical network maintenance

As I work to clear a large backlog of paperwork, archiving, etc., I come across a sleeve of negatives.  No folder, no notes, nothing.  Peering at the negative against a light adds little information.  I can't place the who and where of the content.

I have a small device for digitizing negatives and pull it out and digitize the 22 pictures out of 36 which have enough light for an image at all.  These are not great pictures.  Low light, poor resolution, low contrast, marginal focus.  

I eventually pull the clues together.  These are pictures my youngest son would have taken, almost certainly with a disposable camera some seventeen years ago when he was about ten years old and away at summer camp.  

I send the collection to him via Google albums and get confirmation that that is what the mystery sleeve of negatives is. 

He then mentions something interesting.  He sends five pictures of the friends with whom he has kept in touch.  Within three minutes of my sending the album.  

I am astonished.  Five people from seventeen years ago and three minutes to find and post their current picture.

I go through the photos again.  As best I can tell, there are twelve people among the photos.  He has stayed in touch with five of them, to the point of having recent photos of the five.

It is impossibly improbable in my own context placing myself back at the same age in my earlier time.  Hardly any children had cameras and so pictures taken by kids were relatively few and far between.  In addition, they did not circulate.  One in ten, perhaps one in a hundred instances where the child comes home, gets the photos developed, then sends some back for extra copies and then mails those copies to friends.

In terms of keeping up, you did it by phone or by mail.  If you did that.  Which most did not.  

Economists are accustomed to thinking in terms of barriers to entry.  The barriers to social network maintenance and sustenance were large pre-1990 (cost of photos, time to develop photos, cost of mail, cost of long distance calls, etc.)  Those costs, and therefore the barriers to social network maintenance and sustenance are now, in many ways, close to zero.  

What is lost and what is gained with frictionless communication?

What are the implications for Dunbar's Number when the cognitive burden for social network maintenance and sustenance is dramatically lower than it used to be?