Hi I've had to call 911 myself within the last two weeks. Thought I needed to have a land line or they wouldn't be able to figure out where I was. I was wrong. The minute I dialed in to 911 - bam! There was a tracer signal placed that I could hear. The operator asked for the location of the problem (not my apartment, my insane neighbor down the hall). After I had hung up, about 30 seconds elapsed and there was a tone that indicated, I guess that the tracer had been hung up as well.

Hope this helps!