I hope it is summer but I think it will be october time or longer because I dont see apple releasing a new devices before the 4S has been released for a year for people to be able to upgrade on their contracts or for cheaper at least for those with two year contracts
It will be late summer/early fall just like it has been every year since the iPhone was first released. And just like always, we won't know anything but rumors until a few weeks before it's launched.
I heard a rumour they are going to change the battery to one that only takes 30 seconds to fully charge (forgot what the battery chemical was called). Just a rumour though.