Apple has recently released build 5A240d of the iPhone Beta OS 2.0 to those developers enrolled in the iPhone Developer Program. Also available is an updated version of the iPhone SDK (Beta 3).
The previous version of the iPhone OS (build 9a2151) ceased to function as of 12.01am on April 8th, causing developers across America to be greeted with the "Pink Screen of Death" and display the text "This device is expired. Please install a newer version of the OS".
It took Apple the majority of April 8th to release the updated iPhone OS causing much annoyance amongst developers.
The latest build of the iPhone OS 2.0 reportedly contains a number of fixes surrounding Exchange integration including; additional abilities of receiving and accepting meeting invitations, searching for contacts in the global address list, auto-complete email addresses in the global address list, and setting up an exchange account using Autodiscovery.
The iPhone OS 2.0 is expected to be released to the public in June and will be free for iPhone users but iPod touch owners may pay a small charge.