Exit the room when the mission begins. Enter the opposite doorway. Look on the 
  desk next to the corpse to find a phone.
  After uploading to the second computer, enter the dark office. There is a 
  phone in a unit near the end of the office next to the third server room.
  After the server room ambush, enter the dark area with the white van. The 
  phone is to the right.
  Enter the baggage area. Walk to the end of the room in the left corner on the 
  ground floor to find a phone.
  Enter the other baggage area after the door shuts on you. Climb the ladder, 
  then use the staircase on the right to reach an office. Enter the office to 
  find a phone.