One vulnerability in CSFB (Circuit Switched Fallback) in 4G LTE network will be presented. In the CSFB procedure, we found the authentication step is missing. This results in that an attacker can hijack the victim's communication. We named this attack as 'Ghost Telephonist'. Several exploitations can be made based on this vulnerability. When the call or SMS is not encrypted, or weakly encrypted, the attacker can impersonate the victim to receive the "Mobile Terminated" calls and messages or to initiate the "Mobile Originated" calls and messages. Furthermore, Telephonist Attack can obtain the victim's phone number and then use the phone number to make advanced attack, e.g. breaking Internet online accounts. These attacks can randomly choose victims, or target a given victim. We verified these attack with our own phones in operators' network in a small controllable scale. The experiments proved the vulnerability really exists. The attack doesn't need fake base station so the attack cost is low. The victim doesn't sense being attacked since no fake base station and no cell re-selection. Now we are collaborating with operators and terminal manufactures to fix this vulnerability.