Before you begin, discharge your iPhone battery below 25%. A charged lithium-ion battery can catch fire and/or explode if accidentally punctured.
Power off your iPhone before beginning disassembly.
Your phone's rear cover may have two #000 Phillips screws or Apple's 5-Point "Pentalobe" screws. Check which screws you have, and ensure you also have the correct screwdriver in order to remove them.
Remove the two 3.6 mm Pentalobe or Phillips #000 screws next to the dock connector.
Remove the 1.6 mm Phillips screw securing the pressure contact to the logic board near the vibrator.
Remove the pressure contact.
When reinstalling the pressure contact, be sure to clean it with a degreaser such as windex or isopropyl alcohol. The oils on your fingers have the potential to create wireless interference.
Use a plastic opening tool to lift the speaker enclosure assembly out of the case, being sure not to damage the EMI fingers on the attached Wi-Fi antenna.
Remove the speaker enclosure assembly.
Before reinstalling the speaker enclosure assembly's screws, be sure the Wi-Fi grounding fingers are installed below the lip in the iPhone's metal case as seen in the third picture.
Before reassembly, be sure to clean all metal-to-metal contact points between the grounding fingers of the Wi-Fi antenna and the case of the iPhone with a de-greaser such as windex or isopropyl alcohol. The oils on your fingers have the potential to cause wireless interference issues.
When installing a new cellular antenna, be sure to slide the gold bracket over the ear molded into the speaker enclosure before sticking the antenna down.