What became of them? In the 1950’s, before the advant of communications satellites, live TV was relayed from coast to coast, by a nation wide chain of relay towers.
These towers were on mountains, hill tops, etc., and relayed the signals via high frequency RF (microwaves).
I belive that they were manned.
Anyway, with satellites, these became obsolete-do they still exist?
phone company used a terrestrial microwave relay chain for long distance phone service. it could operate unattended. they provided service to the broadcast industry. optical cable also now handles traffic.
Networks also feed programming to their affiliates with satellite transmission.
Not really an answer to the OP, but this site (Microwave Radio & Cable Networks of the Bell System) has some interesting information on the Microwave Relay system, including routes, equipment, and operations.
Although the site doesn’t seem to have a link of when the system was decomissions, wiki sez
- which seems about right. Of course microwave transmission towers are in use for many purposes nowadays, but alas not for AT&T Long Lines, which is long gone.
Of course I just wasted mega-time exploring that Long-Lines site I posted 
Anyway, the AT&T Microwave Relay system was truly dead by September 1999, when they sold the relay towers to American Tower to repurposed them for Wireless/Cell phone antenna usage.
[QUOTE=Boston Business Journal - Sep 1999]
Boston-based American Tower Corp., an owner and operator of broadcast and wireless communications towers, agreed to buy 1,942 microwave towers and build 1,000 wireless towers as part of a $260 million contract with AT&T Corp.
[/quote]
I wonder if this question should move to General Questions as opposed to Cafe Society - it is about the technology as opposed to the content, and besides my ‘timeline’ answers are probably off and I’d like to hear the real decomissioning story