Wirelessly posted (iPhone: Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en) AppleWebKit/420.1 (KHTML, like Gecko) Version/3.0 Mobile/4A102 Safari/419.3)
it is a limitation of the chipset. However, I think the documentation for the Santa rosa chipset states that it can address up to 8gb once 4gb sticks become available.