They were just talking about it on FoxNews. Last Saturday a man overheard an arabic conversation on his cell phone. The conversation was between two men. One said that he was in the city of sin...prostitution...Unbelievers and other things and that they were going to hit this city during the holiday of Freedom. Or something similar to that. They said that the FBI is investigating but due to the nature of the tip there was little they could do to trace the origin of the call.

I am not faimiliar with cellular technology but would think there is a some, but maybe limited, that they can do to check the informants claims. For example maybe they can start with where he was and what time he heard the conversation and what cell provider he uses and locate the nearest cells. Then they might be able to check computer records and recordings(?) to determine what other calls might have been routed through that site at that time. Due to the volume of traffic though this could be a monumental task.