In general, the GM versions of the iPhone OS released before the final version were identical to the last one and most likely history will repeat itself this year with the release of iOS 4.0 today (probably in the next hour). A proof that supports this theory lies in image presented today with the iPhone 3GS 8GB that comes with iOS 4.0 preinstalled, so Apple didn't really have time to make essential changes in iOS 4.0 before installing it on the new iPhone 3GS model.
If it is identical or not we will find out for sure in the following days, however even if it will not be identical, the final version of iOS 4.0 cannot have major differences compared to the GM version because the developers made their applications based on the GM version of iOS 4.0, so any change could affect the good functionality of the applications and I'm sure Apple doesn't want this.
So, soon we will be able to download iOS 4.0!
