Apple released iOS 6.1.4 for iPhone on Thursday, an update whose sole patch note says, "Updated audio profile for speakerphone." So that's pretty much that.
iOS 6.1.4 iPhone Screenshot
It's an 11.5MB download over the air. The update isn't showing for everyone on TMO's staff yet, but several of us are seeing it in iTunes and on their iPhones.
Apple's KnowledgeBase article for the update mentions a security component, but the Apple Security Updates page has not yet been updated with this release.