Along with the new SDK beta, iPhone OS 4 beta 4 has been released to developers. Current changes are unknown, although there are more wallpapers to choose from.
Coming directly after another build of Mac OS X 10.6.4, Apple is keeping its developers busy today. Since the NDA stops developers from sharing all the updates and enhancements with the public, the exact changes and tweaks aren’t known. Exactly two weeks after the previous beta (beta 3) was released, it is apparent Apple is following a bi-weekly release schedule for these minor updates, with the final GM build probably coming during their WWDC event.