From day 1, I was having problems with the mic when using the speakerphone. I've had the last 4 iPhones so I know how the speakerphone should work. But, every time I was on a call using speakerphone, the person on the other end said they couldn't hear me. Using the phone held up to my ear, over a Bluetooth headset and through the earplugs all worked fine - just a problem with the speakerphone. It didn't happen every single time but pretty much 9 out of 10 times. And sometimes it would work for the first minute of a call and then the person would complain they couldn't hear me. I even called my work voicemail to hear what it sounded like and it was waves of sound with my voice going in and out - completely inaudible. So I took my phone back to Apple over the weekend for them to check it out. They tried to test it with me calling the store phone using my speakerphone but that was nuts because the store was so loud they would never be able to hear anything. They took my phone in the back for a while and then came out to tell me it might be the design of the new mics. Since there was now a mic on the back, they said I should try to use the speakerphone without laying it on its back during a call. I said that was insane because how else would you use the speakerphone function. Eventually, the person helping me out was really nice and said she would just give me a new phone. After restoring from a backup, the speakerphone works perfectly. So it was obviously a hardware problem. In fact, the Apple person said when a mic is failing, it will sometimes have that effect of going in and out. While I was having this problem, I searched Google and a bunch of forums but only found a few people mention it. So it's obviously not a serious design flaw or anything but figured I would post this in the event anyone else is having the same problem. If you are, your phone is broken and you need to get it replaced.