The beta 5 version of 3.0 was released this week. Other than typical bug fixes, some users are claiming that the new version has improved YouTube and removed the iPhone 3.0's MMS feature. Some are claiming that the iPhone can now play high-res YouTube videos via 3G, rather than only via WiFi. There are some rumors floating around about Apple implementing some anti-tethering measures.
We'll keep you posted as more beta 5 features are discovered.
The screenshots below show a before and after comparison of the message settings screen. Notice how MMS is no longer there.