Data communications over telegraph circuits 1936

I perhaps should have mentioned that while not typical, there were customers with DC loops who did not use modems at all.

That is true and has significance. In many ways Alascom (which began only in 1971, as RCA Alaska Communications) made use of Bell System engineering (the Toll Centers and many of the larger installation were in fact originally designed and built by WECO for either the US Army's Alaska Communications System or the US Air Force White Alice Comm System). As a regulated monopoly (for a while), Alascom continued to have close ties to Ma Bell in some ways. But when it came to some things, such as Telex-TWX (and NTI toll switching systems) they were a non-Bell company and therefore went the non-Bell way.

I don't think there was any Telex service to Alaska in the 1960's, though I'm not sure exactly when it was first installed.

It was pulled out of Fairbanks in the mid 1980's, but may have lasted a bit longer in Anchorage. (Any remaining customers in Fairbanks were connected to the Anchorage switch.)

That amounts to using a 931 telegraph system, even if there was only a single 43A1 unit (the last tube type telegraph terminal unit being installed by the Bell System before going to solid state technology). In fact some of the last customers using Telex in Fairbanks would have been connected via a Lenkurt 25D system, which was a solid state replacement for the Bell 43A1 equipment. (The Telex that I used was connected on the remote end to a Lenkurt 23A telegraph system! Probably one of the first transistorized systems produced in the 60's.)

Reasons for using voice channels would be more efficient use of limited cable facilities, or if the distance was too far and the cable bad, or if they were using double wide "high speed" circuits (anything over 75 baud), or of course if the link was a microwave or otherwise used FDM carrier.

By the end of the 70's that was almost universal. Most customers were using some form of computer as a terminal, and were able to store and edit messages, and choose between viewing on a monitor or printing on a dot matrix printer.

That had significance for me personally, because the Pope and President Reagan had conference in Fairbanks back in the early 1980's, and of course that required a huge press presence, which in turn brought a couple hundred of the latest Excel terminals to Fairbanks. Customers used them for a few days... and then they were distributed to every Alascom site to replace older Teletype machines used on the administrative network.

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