i do that too. if it's from a number i'm gonna answer (but don't recognize), i do. and then watch the call timer on the phone and don't say anything until after three seconds. legit callers are always still there, the computers--never are.

if a call rings through that the phone company has tagged in caller id as probably bogus. i just answer and hang-up right away. they don't call back.

You gotta at least start with your most white-person "hello" possible. If its a human they might just assume silence means the call was dropped.