at 20:41 (NTSC) the beginning of chapter 5, Nate Pope (Forest Whitaker) is an Amateur Radio operator with the call sign WB6QLF. QLF is amateur shorthand for "I am sending with my left foot", a reference to someone whose Morse Code sending skill is very bad. This is normally sent as a question "QLF?" meaning "Are you sending with your left foot?" to an operator who is very difficult to understand in Morse. WB6QLF is an actual call sign belonging to a Charles B. Roblin of Victorville.
At 0:21:11 chapter 5 when George Malley (John Travolta) is at Nate Pope's (Forest Whitaker) house showing chairs there is a QSL card in the background with the call sign K6KAP. This is a real amateur ("ham") radio call sign that belongs to a Mach Myovich of Merced, California.