iPhone OS 3.1.3 breaking Wi-Fi for some users

A number of iPhone users are reporting a loss of Wi-Fi functionality after upgrading to software 3.1.3. Based on an Apple Support discussion thread, the problems date back to the update’s release in February, and appear to affect mostly first-generation iPhone and iPhone 3G units, although a small number of iPhone 3GS owners also claimed to have experienced the issue. Some users state that their iPhones now have the Wi-Fi option grayed out, as if no hardware exists to support it, while others say the option is there, but report failure to find/connect to any networks. As a solution, a number of the users report having had their iPhones replaced, which seems to have corrected the problem in some cases, but in others the new hardware also exhibited the issue; Apple itself has posted a support document outlining an issue where there is no Wi-Fi or Bluetooth address listed on the iPhone or iPod touch, but that issue appears to be unrelated to the problems mentioned in the discussion thread.