In the opening scene, one of the callers into the 911 centre states "I think I'm having an overdose and so is my wife" - the line made famous by Edward Sanchez, a policeman who confiscated marijuana from a suspect and then made brownies with it. He called 911 when he thought he had taken too much.
Halle Berry was initially cast in the lead role with Joel Schumacher directing. Schumacher dropped out and was replaced by Brad Anderson. Berry dropped out due to scheduling conflicts but once the start date was pushed up, she returned in the lead role.
Screenwriter Richard D'Ovidio got the idea for the film when his wife saw an interview with a 911 operator on TV. Researching the subject, he visited the Los Angeles Metropolitan Communications Dispatch Center and was surprised to find that it had its own back-up generators, bulletproof windows and a moat.
At 18:57 you can see an article on Leah Templeton in Turners locker. That article says that Leah died on Feb. 26, 2012 and that services (her funeral) will be held on Feb. 27. Obviously there could never be a Newspaper article on her death the same day she died (and it must be from that day as it informs about the services being held on Feb 27)
The original plan was to film in California, taking advantage of the state's tax credits. However, it was discovered that the waiting time for such credits was too long so an alternative filming location was required. The production team settled for Ottawa in Canada and were days away from commencing production when they were informed that the California tax credit backlog had been cleared and that they could film in the state after all.
In the final fight scene where Jordan is thrown to the ground Halle Berry hit her head on the concrete. The on site medics said she she only had a bruise and a bump on her head and was okay to continue filming, but noted she could have suffered a brain injury if she landed differently.