Big day for third party developers, as Apple just released Beta 4 of the Apple software development kit (SDK). And with the massive update package, it also released the Xcode integrated development environment (IDE), the newly renamed iPhone simulator for the computers coupled with OpenGL ES rendering support, plus tools and samples to toy with.

But you probably already knew that, if you've been enrolled in Apple's developer connection program. The Cupertino-based company supposedly sent in e-mails to those concerned, with a message that contains this passage:

The fourth beta version of the iPhone SDK includes Xcode IDE, iPhone simulator with Open GL ES support, Interface Builder, Instruments, frameworks and samples, compilers, and Shark analysis tool.

We can't quite yet tell if build 5A258f resolves issues reviewed from build 5A240d (a.k.a. Beta 3), but what we're getting from dev streams on the Internet is that Apple is strictly enforcing code signatures (yep, farewell unsigned homebrew code) and that UIFont just got a long-called for overhaul.

Also some speculations of background application support have been sighted, though we haven't gotten any real firm confirmation.

What we might be more sure of is that like previous versions of the beta builds, you'll be warned about the Beta 4 installation locking your iPhone to permanent test mode. Also, if you haven't pre-activated your AT&T account and load Beta 4, you can't activate the phone on AT&T's network.

More updates on the iPhone SDK as we get them. In the meantime, you can reach the Developer's Connection via the link provided below. Just sign up and you're free to download the gigabyte-heavy package.