At some point, our 18 month old decided the phone tasted great. We didn't realize it immediately, but she had managed to get so much of her saliva into the head phone jack that the phone believed it had a microphone attached.
Consequently, any subsequent movies of her didn't have any sound.
I wasn't sure my analysis was 100% correct, so I didn't feel like handing the phone over to a service technician. Considering the part was only $25, I didn't want to pay someone else to complete the diagnosis.
The iFixIt guide was precise and detailed enough to walk me through the entire process. It took a little more time than I had suspected, and I had to dissemble the phone twice because I didn't install the silent switch properly, but the phone works again.
The removal of the battery is less clean than it was implied in the instructions. The battery is apparently made up of a soft metal, so it will bend... it will bend and deform a LOT. The instructions to simply "pry" the battery off the adhesive doesn't quite convey the full "experience" and that care should be taken to not deform or bend the battery too much. In fact, instead of the plastic splunger, a thin spatula tool would have been more appropriate to get underneath all of the battery and gradually pull it off of the adhesives on the lower right corner. Of course, I'm not sure such a tool exists.
And oh... remember that the phone is face down when installing the silent switch back in... really... it's face down, darn it! :-)