Hi.
The old POTS sturdy single pair wire coming from the pole to a dwelling was, decades ago, solid AWG 18 with a thick real? rubber sheating, stiffer with poor flexibility, very weatherproof and silverish-copperish color conductor. Is such still available and what specifications name to order it ?
It is not the pure? copper AWG 24 running indoors as red-green-yellow-black.

 

'Telephone Cable'?

https://www.electricalworld.com/en/Zexum-3-Pair-6-Core-Round-White-CCS-Telephone-Cable/m-719.aspx

 

Is it CCS copper clad something cable ? That sounds right, but single not-twisted pair...

 

Don't think you can still get the old Western Electric line cables.
https://www.telephonecollectors.inf...y/catalogs-manuals/bell-system-we/we-catalogs

Even the modern direct replacements seen to be discontinued.
https://www.anixter.com/en_us/produ...change-and-Distribution-Cable/p/F-02P22DZ-SUP
https://corpapps.anixter.com/DocLib1/B5ON04CD/$file/TelephoneCables.pdf

 

Seems the "S" in "CCS" is steel ! Makes sense. And is available in 2 or 3 gauges ( https://www.newtechindustries.com/a...l-1-pair-18-1-2-gauge-1000-foot-popbox-adp-d/ ), in PE or PVC jacket. Now, there is more of the alphabet :

 

Any Physically Suitable Conductor pair is OK, what is important is that it should be 600 Ohm Balanced Pair.

 

For the external telephone connection, as described above by those who know what you mean, the description is "telephone drop wire" or "telephone drop cable", followed by either "single pair" "two pair" or "Four pair", depending on your requirements. A caution is that there is a very similar looking product that has two fiber optic cables inside, that are as stiff as the hard-drawn copper wire or the copper covered steel wire. But they simply do not work for an electrical phone hookup. The fiber optic stuff can not be spliced without the splice connectors and expensive tools.