"ometime during the late evening hours last night, Apple released iPhone OS 3.0 beta 5 for developers. Surprisingly, instead of the usual two week beta release, beta 5 was only released eight days after beta 4, possibly indicating that Apple may be putting the pedal to the floor to get the iPhone OS polished and ready for the WWDC.
At this time, the only known changes in beta 5 are the addition of parental controls, the blocking of editing the iPhone's carrier file (no more tethering), and also the blocking of MMS on AT&T. Could all of this be at AT&T's request? It is all speculation at this point."