The Talking Tombstone speaks to passers-by. I feel it would be cheaper to get a number of those toy parrots with the voice mechanism and sit them on top of the stone. Of course, they might say the wrong thing.

Gizmodo (German / Deutsch, which has further links) suggests using it for insults:

bq. Noch in der Grube kann man mit diesem sprechenden Grabstein seine Nachwelt beleidigen, Verwandtschaftsstreitigkeiten bis zum Ehrenmord schüren und generell das letzte Wort behalten.

I don’t think one could get away with that in Germany, although it might be hard to pin down a defendant.