We call this plant Pera (Pear) in the Dominican Republic. The autor of the picture calls it "Pyrus Communis" but it might be wrong due to the round shape of the fruit. I used to eat this when I was kid back home. the fruit is sweet and has like 4 seeds. What do you think? http://home-4.tiscali.nl/~t794614/azfauna/drfruit/drfrpera.htm
Sorry, don't know. Can you get photos of the leaves and flowers? That might help with identification.
Thanks everybody but somebody already told me. It's called Casimiroa Edulis http://www.tradewindsfruit.com/white_sapote.htm