The ending... (MAJOR SPOILERS!)

If this movie confused you, then this might help. For people who haven't seen this movie, then you probably don't want to read this. I think I've figured out the movie well enough to the point that I could explain it, but this movie had so many plot holes that it's hard to fully understand most of the movie.

The old man at the beginning of the movie (presumably) taps into Alicia's phone so that he causes the loud electronic sound to go off when he would call her. The plot with Franklin has absolutely nothing to do with the old man, or the phone just to mention. During the middle of the movie, there is a reporter on the radio that says that a murderer is on the loose who kills people after the victim receives an obscene phone call from the killer. After Franklin is shot by the police, Alicia receives more and more phone calls until she breaks her phone. Then, she hears the electronic sound behind her, and she spins around... The next morning, we see the old man (the same one that was in her apartment at the beginning of the morning) leaving her apartment. Okay, here is how it all seems to me.

The old man is the killer that is mentioned on the radio, not Franklin because after Franklin dies, the phone calls continue. After Alicia breaks her phone (due to going hysterical from the electronic sound), and she hears the electronic sound again, she spins around to find the old man in her apartment. When she realizes he's in her apartment, he murders her. He leaves the apartment the next morning while we are given no clue as to what happened to Alicia but her fate is pretty much clear.

Ha, made you look!