Tonight Apple released a revised version of iOS 5.1.1 for only the iPhone 4.
The original build of iOS 5.1.1 is labeled 9B206, while the new build is labeled 9B208. As indicated by the build number, the iOS release is two builds newer and most likely has a small fix.
At this time the revised build is restricted to the GSM version of the iPhone 4 and is not available for any other iPhone device.
Additionally, Apple has not described the changes that are included in the revised release.