Never answer a ringing rotary phone because there’s madness on both ends, but Rick does anyway and has a heart to heart with his dead wife, and the interpretation is that this is a kind of working through of the grief and forgiving himself, which would be right except that this is a show about zombies, so it’s wrong.
His zombicidal rage in the prison was working through his grief; the phone call, however, came after that was all over, and so the starting point of interpretation is that this is the single instance of mourning in the show that is not mediated through the experience of zombification– i.e. denial of death– but through a connection to something else that carries on after death, the essence of a person, the exact part lacking in zombies.
In the show when you die you don’t die, you continue as a zombie, and then you must be finally put down, terminally terminated; so if he believes he talked to her– as if in a dream– then the point isn’t that she forgave him but that she still exists, just as the body survived, the soul survived as well.
The key is the telephone, it is the single mediating device that he knows just enough and not enough about that it would plausibly still be operational, it has copper wires and gears, after all, (remember the old timey computer in Lost?) not like a cell phone which he knows couldn’t work, or a material letter which is similarly unimaginably impossible. So while he knows perfectly well he could not have talked to his dead wife’s spirit on the telephone, he’s created a split which he can forever avoid confronting head on: that what’s impossible isn’t her spirit but that he talked to her spirit on the telephone– rather than the phone mediating an impossible communication, it becomes the “sink” for the doubt, leaving all else floating uncritically, possibly….
And yet still they do not call them zombies.