After doing some additional research, it turns out that sugar apples (sweetsop, anon) and cherimoya (custard apples) are actually two different (but very closely related species). The sugar apple comes from Annona squamosa, while the cherimoya is from Annona cherimola.
This review is for sugar apples. I am not sure how different the two taste, but will have to pick up a custard apple when I have a chance.
Sugar apples are originally from the tropical Americas, but have been introduced to Asia and many other parts of the world. Sugar apple trees are small to medium sized at 10 – 20 feet with a wide variety of cultivators available, some even seedless (not this one, it had seeds in it as you can see).
When sugar apples are first purchased in the store, they are generally hard and unripe. Given a few days, the sugar apples will ripen, with the fruit becoming more fragrant, becoming soft to pressure and the areas between the scales turning white. To eat the sugar apples, cut the fruit open and spoon out the flesh. Avoid the seeds, turns out these are actually poisonous. Sugar apples taste like a very sweet melon (at least to me). Buy one, try it out and let me know what it tastes like to you.