Apple Release iOS 4.1 for Developers [Download]

Apple has announced to developers that iOS SDK and iOS 4.1 beta are now available from the iPhone Dev Center.

Apps built with iOS SDK 4.1 beta should only be tested on devices running iOS 4.1. Make sure to read the Xcode 3.2.4 Readme and the iOS SDK 4.1 beta Release Notes before installing and downloading these new releases.

download it here.

Update 1: Some MacStories users announced that Game Center is back? May be? GO ahead and download it! I'm downloading it right now to try it :)
Update 2: iOS 4.1 didn't fix Receptions issues, Check details posted here.
Update 3: The modem firmware has been updated to 02.07.01 from 01.59.00. No word on if people are having any actual signal improvements beyond the cosmetic changes.
Update 4: First Screenshots of Game Center

Update 5: MacRumors member “macduke” posted an image of the old signal bars compared to the new ones

I took the images from 4.1 and compared them to my 4.0 iPhone 4. I then did an opacity comparison and used the marquee tool to select the areas of each and color the difference in green. This is the result that I got, after blowing up the image x 4 so its easier to see. They have effectively made the smaller bar twice as tall! As tall as the old 2nd bar.

 UPDATE 6: You can now turn Check Spelling off in the Keyboard preferences:

 UPDATE 7: You can now add Favorites in the Phone app as FaceTime or Voice Call.

 UPDATE 8: MuscleNerd confirmed the watermark rumors are simply not true. Good news, jailbreakers.