While Apple's official line is that the only 3rd party iPhone development will be on the EDGE-crippled Web 2.0 "SDK", behind the scenes, there is much more going on. Apple has been furiously working with their partners on games and applications for the iPhone/iPod and the standardized Human-Interface Controls that will go along with them. For instance, EA is currently porting their iPod lineup to the OSX iPod/iPhone platform to be sold along side the classic iPod OS versions. Other big developers with strict confidentiality agreements are also on board.
Apple is specifically looking to replicate the model of TMobile's successful SideKick application development and distribution platform (although obviously not in the Sidekick's Java). Apple has even brought in some of Danger's (SidekickOS creators) application development team to help with the architect