Recently published operator profiles by Apple refer to iOS 5.1 and a release date of March 9, 2012. The profiles are intended for various operators in Japan, France, Finland, Greece and Sweden and will make sure the iPhones will connect to the specific network after an update.
The iOS 5.1 update has been in the works for quite some time, its third beta has already been seeded to the developers but there is nothing official on the launch date yet.
Since those carrier profiles are published by Apple, March 9 is Friday, which is the day of choice for this sort of launches, and the timeframe matches the rumors of an iPad 3 announcement in early March. So I guess, this is one of the most reliable leaks so far.
Source | Via