Thanks Brian. I had not thought about the issue of two flight numbers on different airlines with the same flight number. And, I would imagine that is true even not only in an area, such as Las Vegas, but if SWAxxx is talking to one "center" and UAxxx (where xxx is the same for both) enters that same center's control area. Back in my UA flying days, I'd hear one center warn two aircraft when they had similar sounding numbers under a single controller.

The flight caster web site really does the trick. A very handy web site that I will be adding to my cell phone.