Apple iPhone 4 doubles the operating memory of its predecessor to 512MB
Nonetheless it was made clear in developers sessions during the WWDC 2010 that the iPhone 4 will ship with twice the memory of the 3GS or the iPad. It makes sense to expand the RAM, since the new version of Apple's mobile operating system, iOS 4, will ship with multitasking capabilities, which will undoubtedly require more memory.
Apple iPhone 4 Specifications
source: Circuit Breaker via CNET Asia