IPhone – Troubleshooting an iPhone 4 connected to wifi, but can’t connect to the internet

The expected behavior is probably for the phone to stay on WiFi as long as it can connect, and then switch to 3G; as of iOS 5, I don't think the capability is there to automatically notice a dead WiFi connection and switch to 3G. So what you're seeing is perhaps a lack of functionality, but it's not strictly speaking a bug.

I can't really see Apple making that the default functionality, though. They'd get a lot of flak for making the iPhone too smart; nerds would complain that they don't have control. If it was done, it would probably be an option.

It also would be very difficult to do well automatically. How does iOS know a connection is bad? What exactly does "when WiFi stops working" mean?

• Lack of public internet access? Windows 7 (and maybe Vista) does this by requesting a text file from Microsoft's website with predetermined content; that's how it knows if your connection has internet access or not. But what if you're on a network at work that only offers access to intranet sites, and not the public internet?
• Lack of data transfer despite network requests going out? What if you're repeatedly trying a site that's experiencing a lot of traffic? How many repeated failed requests mean a bad connection?
• Long response times for outgoing requests? How long is too long? It could be averaged over time, but where's the threshold?

It could probably be done, but it would be difficult to do well, and the gain in widespread user satisfaction probably isn't that huge in comparison to other things.

If re-setting your network connections didn't help, it could be a hardware problem.

Depending on when it was made, it could be that your WiFi chip inside the phone has pulled (or, rather, is in the process of pulling) off of the circuit board. Late 4S models also had this problem, and here's how it manifests (progressively):

• Very slow speeds / drops connection to the network intermittently
• Stops seeing most (or all) networks, but the WiFi button still works, it's not grayed out
• Can't turn WiFi on at all, the button is grayed out in the settings menu - but the WiFi button in the control center might appear to work.

If your phone is under warranty, then take it to an Apple store and have them replace it. Believe it or not, the repair is quite easy, so if it's out of warranty and you know of a place that fixes phones, they've probably got some spare chips and won't charge too much. Apparently, it's a manufacturing defect, so a repaired phone fixed by someone that knows their stuff could last quite some time.

This has only been a problem with certain 4S and 5 models, you'll see a bunch of people reporting it if you search for something like "iPhone in freezer" - because (believe it or not), putting your phone in a Ziplock and then freezing it for a few minutes has been known to fix the problem for a short time (though I don't recommend doing this).

AFAIK, this isn't an issue with 5C, 5S or recently (as in the last year) manufactured iPhone 5 units. Could be a good opportunity to upgrade, even if you manage to get it fixed.