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.
Exit is an object within the Matrix that is used to allow Zion operatives leave and have them return to their consciousness to their body lying at rest in their hovercraft. Operatives must find and use a proper exit that allows their mind's communication with the Matrix to be safely disconnected.
In the Matrix film trilogy, the differences between cell phones and wired telephones were never discussed, but viewers are led to understand in the first minutes of The Matrix that a "land line" phone is needed to leave the Matrix.
Explanation why a hardline is needed:
Sinclair: Why were they only able to jack in through hard-lines, but still able to communicate over cell?
WachowskiBros: Sinclair, good question! Mostly we felt that the amount of information that was being sent into the Matrix required a significant portal. Those portals, we felt, were better described with the hard lines rather than cell lines. We also felt that the rebels tried to be invisible when they hacked, that's why all the entrances and exits were sort of through decrepit and low traffic areas of the Matrix.
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.
I think the real reason they needed to use a landline was because the Wachowski Brothers needed our heroes to be limited in some way. If they could get in and out of the Matrix anywhere at any time on their cellphones, how can you have tense scenes like when Trinity and Neo try to escape the subway, or when they all get attacked in that run-down apartment building?
I think it has more to do with the fact that to get into the Matrix required an internet connection by which the avatars for Neo, Morpheus et al could travel.