25 - 45 minutes
My iPhone 4 got dropped into a piece of cake and frosting got into the bottom left speaker opening. I tried to clean it from the outside but the sound from the speaker was still muffled. Ultimately I found the repair guide on iFixIt.com and decided to take the phone apart and attempt a more thorough cleaning. I am eligible for an upgrade on my phone so I figured I had very little to lose. Using tools I already had, I removed the battery and the speaker housing and was able to clean the speaker port completely with a q-tip and rubbing alcohol. While reassembling the phone however I didn't notice the little ground "fingers" on the cellular antenna and broke two of them. The phone worked great after reassembly (including the speaker) but I decided to get the right tools and replace the antenna anyway.
With the right tools, the removal of the speaker assembly and replacing the cellular antenna were much easier. My phone is back together and functioning as if it never had any issues.
When tackling a repair on this complex of a phone, don't rush things. read all the little notes on the repair guide, and limit the caffeine intake before hand. :)
Beyond that, I was pleased with how straightforward the repair was.
SIM Card Eject Tool
Mako Driver Kit - 64 Precision Bits
iPhone 4 (GSM/AT&T) Cellular Antenna