The expected Windows Phone 7 May update is already available and most of the users should have access to it. It does only one thing – fixes security vulnerability with fraudulent third-party digital certificates.
The update is not an OTA one, because it packs every previous WP7 update (incl. the March one that brought us the copy/paste and other good stuff) and it’s large in size.
The SIM-free devices can get the update through Zune right now. According to Microsoft the update is already in the carrier hands too so if you don’t have it available yet (in Zune) you’ll get it soon or bundled with the next update.