Context: Stu Shepard (Colin Farrell) is an arrogant New York City publicist who is contemplating cheating on his wife Kelly (Radha Mitchell). He calls Pam (Katie Holmes), a young actress, from a phone booth on a side street. When a delivery man (Dell Yount) tries to deliver a free pizza to the booth, Stu rudely dismisses him. After the phone call with Pam, the phone rings and Stu answers it. The caller (voice of Kiefer Sutherland), says that Stu should have accepted the pizza as it would have "kept his strength up for what comes next". He warns Stu not to leave the booth. Stu, again dismissive, is skeptical toward the mystery caller. The caller says that he will say 'hi' to Kelly for him, then hangs up, leaving Stu visibly concerned.The unseen man calls back and reveals that he had previously setup two other dishonest individuals in a similar situation, where he gave them a chance to redeem themselves but since both refused he had to kill them. One was a pedophile, and the other was a business executive who used inside information to cash in his stock options before the company share price collapsed (and refused the caller's request to share the proceeds with regular investors who got burned on that stock). The caller tells Stu that he must tell Kelly and Pam the truth: that he is cheating. The man calls Pam, puts Stu on speakerphone, and he tells her that Stu is married and does not want anything with Pam except to sleep with her. He then tells Stu to call his wife and tell her the truth, or else he will. Angrily, Stu does so.Before he has a chance to tell Kelly the truth, Stu is distracted by three prostitutes who want to use the phone. The prostitutes become hostile due to Stu's refusal to leave the booth, and they start banging against the glass. Stu becomes agitated and finally hangs up on his wife and yells at the prostitutes to leave him alone. As the three girls leave, the man calls and warns Stu that if he hangs up again, he will shoot him. Stu does not believe him but is convinced when the man cocks his rifle. Stu gets scared, warning him that if he shoots, the cops will arrive. However, the sniper proves him to be wrong by shooting a toy robot next to the booth without anyone noticing. The caller continues to mock Stu's faith that the caller is not capable.The situation escalates further when the prostitutes and their pimp, Leon (John Enos III), approach the booth and demand that Stu leave. Terrified that he will be shot, Stu refuses. The impasse between Stu and Leon escalates to the point of Leon breaking into the booth with a bat and attacking Stu. The sniper tells Stu he can help him and Stu says "yes". Leon is shot in the back by the sniper, horrifying the prostitutes, who accuse Stu.The police arrive and Stu is instantly the suspect. He doubts that they will find any evidence to suggest his guilt to the murder, but later finds out the sniper has planted a gun in the phone booth's roof, on top of the light panel that could be used as evidence in Leon's murder. Captain Ed Ramey (Forest Whitaker) arrives tries to negotiate with Stu to exit the booth but he says he cannot get off the call and he is talking to his "psychiatrist". Multiple news vans arrive, and reporters begin filming the situation, putting pressure on the police to deal with the situation without appearing trigger-happy. The caller continues to taunt Stu by telling him to take hold of the planted gun, or he would "Blow him (Ramey) Away!" but Stu refuses, knowing the police will likely shoot him.Kelly arrives at the scene and the sniper makes Stu confess to her about his infidelity, which Stu does. The man asks Stu to choose between Pam and Kelly, threatening to kill one of them to eliminate further temptation. The unseen caller tells Stu that there are policemen right now trying 
 Question: Who does Stu have to call?
Output: pam