Apple has released an updated version of iOS 5.1.1 for the iPhone 4 GSM. The build for this latest version is 9B208, while the previous version was known as 9B206.
The release is only for the iPhone 4 GSM. It is likely a small bug fix given its slight build number difference.
Either way, it is advisable for you to hold off on updating until given the all clear is sounded with regard to jailbreak compatibility. Make sure your save your iOS 5.1.1 SHSH blobs so that you can take advantage of a future downgrade if the need ever arises.
However, this latest version will reportedly not update your baseband.
Source: iDownload Blog