It isn't *that* bad
Just my personal opinions of course...
Apple is doing a last minute rush to get the iPhone out the door. This isn't any secret: they are releasing the very last biz day of June, they announced the Leopard delay was because of iPhone, etc. A full developer SDK is tough to put together, and it just isn't as high on the priority list as getting the included apps solid for ship. I do believe there will be a full iPhone SDK, eventually. If Apple doesn't plan to do it, they'll probably start once the community begins figuring things out itself.
With that said, I don't think the iPhone picture right now is as bleak as some people here make it out to be. Imagine a version of Meebo specifically for the iPhone- that could handle IM services pretty well since OS X can multitask and leave the site/app open in the background. I think a lot of things like that will start popping up to fill in the immediate IM / MMS style gaps.
Of course, without a full SDK or full "unofficial" tear-down of the device, applications like Skype or smoothly animated games aren't possible. I'm sure AT&T doesn't want Skype (or its equivalent) happen, but it will. Apple needs to realize that true 3rd party apps are going to happen with or without their help, and if security/stability are truly important to them- they need to push out a real, supported SDK soon after the release.