I thought the vary same thing!! Why on earth would AA call to tell me my miles are expiring, why not just let them expire?? The 800 # she left goes to the AAdvantage department (maybe others here have heard of the same call) I listened to the message again and she does say for $161 she can extend them for 18 more months, so that must have been why it is worth it to them to put someone on the phone and make those calls?
The number my caller ID box captured was 800-882-8880