I imagine there were ancient pod people powered phone switch rooms scattered throughout the ruins in The Matrix movies, and that's why certain phones were still viable years after the sky was torched... What I don't get is how virtual people navigated from one physically wired phone location to the next. Their Zion contact would call them with a working land line and the people visiting the Matrix virtually traveled to its physical location. I get the copper circuit in and out part, but I don't get the physical entrance/exit bit. Trinity had to run to a landline. Why and how did she get from the line she jacked into to the line she jacked out of? How did that work?
You seem to be confusing parts of the real world versus the computer world. In the real world, crews tap into wireless signals to enter the matrix. While in the matrix, certain phones are hacked to create a link through the matrix to allow their consciousness to return back to their body.
Explanation why a hardline is needed:
As a side note, remember that this was 1999. Actual wireless technology was in its infancy. Wireless A and B had only come out that year. Wireless G wouldn't have been released until 2003.
Between these real-world facts, the findings in the wikia link, and the response from the Wachowski brothers, that only answers why hard lines were used--not exactly how they worked. I'm not sure there's a clear answer to that, since it was only a plot device in the film and not explicitly explained anywhere.