iPhone's sixth SDK has just been released, adding support for the latest iPhone OS and fixing various bugs. You'll have to update to Leopard 10.5.3, which was released earlier today. That's right, you HAVE TO. Not sure why, but that's what Apple's saying. [Apple]
The reason each update is big news is because shortly after each update, the hacks out there will pick the code apart bit by bit and feed us new iPhone rumors based on the tags embedded in the code. Maybe this version will have a toggle for CDMA/GSM.