I don't think there's any doubt that it's 256 MB:
1) They didn't specifically state an increase in RAM at WWDC. If they had increased the RAM, they certainly would have boasted about it.
2) The iPad only has 256 MB of RAM and it has very similar resolution and chips. The iPhone would only need less than or equal to the amount of RAM in the iPad. So if it's good enough for the iPad, then it's good enough for the iPhone.
3) The way they are implementing multi-tasking means they really don't need more than 256 MB. And before someone mentions Safari reloading tabs, we already know this isn't because of RAM. Other browsers such as Atomic can keep multiple tabs open without reloading.
So it really doesn't matter if the e-mail was fake or not because we can safely assume that the iPhone 4 has 256 MB of RAM.