I checked with Mastercard and found out I have this coverage too. Never knew! I'm sure i could have used it before as I'm always buying gadgets which invariably drop in price.
Unfortunately I bought my iPhone the day they came out...over 60 days ago
Looks like a lot of people have had the same idea though. Found this at tuaw.com:
Readers report that calls to the American Express Return Protection line (1-800-297-8019) are being met with mixed results. Some readers say they are now accepting claims concerning the $200 dollar iPhone price drop, others have had less luck When I called, I was told that customers would be sent to a claims examiner to determine whether the difference in purchase price would be covered. I placed a call to Molly Faust, the American Express Vice President of Public Affairs and Communications for U.S. Consumer Card and Customer Service Delivery. She told me that she was already looking into this matter and promised to get back to me.
According to one TUAW reader, a protection-line operator said "the number of calls we've received about this is utterly insane."