I think I have a clue. My wife's iPhone 5 mysteriously had the speaker go dead on her a little while ago. She is a heavy user of the speakerphone, so I thought little of it — just not a robust-enough part. She took it in to an Apple Store and they replaced the phone. After about a month, the speaker stopped working on the new phone. This time, the Apple Store employee took her phone to the back and returned the same phone to her with the speaker now working. My bet is if I look on her phone, I will see that it is already running 6.1.4 (or a custom build of 6.1.3). So it was not so widespread a problem as to garner significant public attention, but it was costing Apple enough that they tracked the source of the problem down and fixed it. That's my best guess.
Entirely possible, Anthony - thanks for the note!
I just purchased my iPhone 5 on 6/25/13 and I am a frequent speakerphone user...I am constantly being told that I can't be heard or my voice sounds mumbled. I did the update. Problem is not fixed. I called Verizon and they said I have a 14 day Waiver and to return the phone for another one. I'd prefer to just fix the issue. My music sounds fine! I'm able to talk via handset and be heard fine. It's just the speakerphone.
Hmmm, I never installed 6.1.3; will I be able to go direct from 6.1.2 to 6.1.4?
I don't know, to be honest, and it might be different if you update via iTunes versus on the iPhone. Worth a try, or at least it is if you think you need 6.1.4, which seems rather unnecessary for most people.
I did not update as the technician at our local Apple reseller said it made his voice sound like Darth Vader to his mother on the other end of a call. MacRumors noted a few others who had the same trouble.
Guess I'll wait for 6.1.5.
I have a problem on my iPhone 5 where people have a hard time hearing me unless I have at least 3 bars. My wife updated her 4S from iOS 5 to 6 and claims to have the same problem now. I've wanted to write something about it, but I didn't know if it was a common problem.
But sounding like Darth Vader...that sounds like a feature, not a bug!
I use the speakerphone a lot. If anything, the maximum volume seems to be lower, so I don't see this as much of an improvement, possibly the opposite.
For what it's worth, I usually do updates through iTunes as they tend to be combo-type updaters rather than smaller, less-thorough delta ones.