5 - 30 minuten
Liquid got into the top of my iPhone while it was sitting in the dash of my car. Unknown to me one of those scented liquid containers had spilled into the area where the top of the phone was laying in. This caused the camera and speaker to fail on the unit.
Took it all apart (Instructions did not match my exact iPhone 4 but they were close enough) and found that the speaker and camera were just saturated in this liquid (smelled good though). While taking it apart I noticed there was a lot of liquid still inside the phone and I did my best to use Q-Tips and compressed air to clean up and remove as much as I could. Put everything back together with the new battery and everything worked on the first power up except the speaker but I found out a very funny way to fix it from another forum.
If you are having issues with the ear piece speaker on the phone sounding muffled there is a trick to fix it. Put your mouth over the speaker part of the phone and suck in heavily quite a few times. After that test the phone to see if you can hear better. After doing this about 50 times the speaker worked perfectly and I have had no issues since then.