In Season 5, why does Nurse Jackie keep calling Charlie?
Charlie died of a drug overdose in the final episode of Season 4, so this doesn't make any sense to me.
I was trying to figure out the same thing. Maybe it is a sort of "therapy" for her. The only explanation is that his father didn't close Charlie's phone account; therefore, she is still able to call Charlie. Charlie definitely died last season.
According to the press release for the second episode of season five, “Luck of the Drawing”:
Jackie, overwhelmed by the day, downloads to the only person who will understand. She calls Charlie Cruz’s voicemail.
There is also a pay-off later in the season, in the fifth episode, "Good Thing":
Later that night, Jackie and Frank skip the fancy restaurant in favor of a pub. It’s a great date with a good guy. All is going well until Jackie’s phone rings: It’s Mike Cruz, urging her to lose the date. She follows Cruz to his apartment and he confronts her about calling Charlie’s phone. He falls apart talking about Charlie. A moment of shared grief turns into connection and need and they have sex.
Jackie meets Cruz in his apartment where there are photos of Charlie all over the place. He tells Jackie he is having a hard time getting over Charlie’s death. He also confesses to Jackie that he could not get rid of his son’s cell phone and has heard all of the messages that Jackie has made over the past few months. He shares with Jackie that she is the only one who understands and he needs her help.
Because Jackie is not ready and able to deal with AA and having a real sponsor, so instead she calls the now deceased Charlie. It's her form of therapeutic release.
Maybe it's to hear his voice on the answering machine