We try as hard as we can to stay on top of the scams going around, and I think that this may be another:  a call from (303) 747-5508.

I am not certain how the scam works, but I am guessing that it is a robo-call to see if your number is a "working" number, so that it can be added to a list to be sold to telemarketers.

When I received the call (Caller ID said it originated in Colorado), all I heard was a computer-generated female voice saying "Goodbye".

Best bet: don't answer calls from numbers you don't recognize.  If it's important, I'm sure they will leave a message.