I don't recognize that meter, what is it?
I started off as a apprentice lineman and worked in pole line construction and got bore after 15 months so I transferred into customer services I&M,(installation and maintenance) for the next 13 yrs, we had little Triplet VOM to use for trouble shooting
I have two of them in my shop still Along with a Fluke 87 digital VOM hat was provided to me to evaluate for field use, it works good also
Direct current is very basic, no magic as long as you under stand the theory on current flow. All the phone companies I know of used A.C. for ring current and D.C. for talking on.
That was over 24 yrs ago when I was RIF so I have no clue what technology is being used now, especially on wireless and Smart phones