I'm covered some common tips to resolve Wifi connection issues in my previous post. However, not all users can benefit from it. Many believe the Wifi issue is related to jailbreaking. Based on this 44-pages long discussion thread at Apple.com, I’m very sure that the connection issue is unrelated to jailbreaking but possibly due to the buggy iPhone 3.0.

Quite a number of iPhone 3G owners that they failed to connect to Wifi after upgrading to 3.0. Even some users are able to connect to Wifi, they also experienced connection drop or unstable Wifi connection. Here are a few Wifi connection issues reported in the discussion thread:

I have exactly the same problem. Wifi drops when the phone sleeps, and needs to be reset by toggling the wifi on-off switch. Scanning for the network is also flaky. It worked perfectly prior to installing the update. We need a fix, Apple!

Before updating, Wifi worked flawlessly; at times even better than my macbook’s.
After the updating, my iPhone does not discover my networks anymore. I have made it recognize my home network, however, by getting closer to the router. But since distance has never been a problem, it definitely shouldn’t be now.

I’m using a 3G iPhone, and upgraded to 3.0 yesterday. Since then I’ve been unable to join any wifi network at all.

The wifi dropping has been driving me nuts. It’s only started since 3.0. Before, it has always stayed connected, never had conflicts on the network, and was never an issue. But since 3.0, like a lot of others, it can’t hold the connection for more than 20 seconds without releasing.

But the wifi issue is only found after upgrading to iPhone 3.0 and experienced on iPhone 3G only. Upgrading to firmware 3.0.1 does not resolve the issue. The problem may be caused by the baseband update in 3.0. Or due to overheat of Wifi chip. Some users even tried to put their iPhone into freezer for a minute. Take it out and find they pickup the Wifi signal again. (Don’t try it as it will void your warranty). There seems no concrete solution or workaround for this problem. The best way is to take your iPhone back to Apple Store and ask for a replacement or wait for iPhone 3.1 update to fix this issue. But before that, you can also try the following possible solutions that have been reported successfully for some users:

  1. Turn off Push Email in Settings and restart your iPhone
  2. If you can see your network in the list but it doesn’t connect, press the little blue arrow and then tap “Renew DHCP lease” or “Forget this Network”. Try to connect to Wifi again.
  3. Reset network settings (Settings -> General -> Reset -> Reset Network settings)
  4. Reset all settings (Settings -> General -> Reset -> Reset All Settings)
  5. Restore your iPhone with latest firmware and setup as a new phone in iTunes
  6. Put your iPhone into Airplane mode and then turn on Wifi
  7. If you’re using 802.11n router, try to change it to support “G” only instead of “mixed” or “N” protocol
  8. Disable Wifi router security and see if you can connect without password
  9. If you have to use Wifi security, try to set your Wifi security to WPA2
  10. Change your Wifi router channel to 1, 6 or 11 or simply change it to other numbers that may work for some users
  11. Upgrade the firmware of your Wifi router

Deerman on the discussion list also proposed a method to resolve the issue and you can also try it out:

1. Change your WLAN-/WIFI-station to non secured (no password)
2. Try to connect your iPhone – most probably it won’t connect
3. Change airplane mode to “On” and wait 10 sec
4. Change airplane mode to “Off” and wait 10 sec
5. Change airplane mode to “On” and wait 10 sec
6. Change WIFI to “Off” and wait 10 sec
7. Change WIFI to “On” and wait 10 sec
8. Try to connect – most probably it will connect!
9. Now change your WLAN-/WIFI-station to secured 128-Bit-WEP and give it a password
10. Change WIFI to “Off” and wait 10 sec
11. Change WIFI to “On” and wait 10 sec
12. Try to connect with your new password – most probably it will connect again.

If none of the above works for you, I suggest you to contact local Apple Store for help.