IPhone – How to upgrade the jailbroken and unlocked iPhone 3GS to 4.2

It may still be a hardware issue -- I had a similar problem last year. But since you say that your phone sometimes does see a wifi network, there's hope that the hardware is okay.

First, follow the comments posted here to make sure you're running a completely normal OS without any hacks or modifications.

Then, here's Apple's description of how to reset the network settings.

Lastly, if it still won't work, check my link above.

Among other things:

• Free “Find my iPhone” (don’t need MobileMe) —> this requires an iPhone 4
• Safari allows you to search inside the page
• You can assign different SMS/MMS/ALERTS to different phonebook contacts
• AirPlay / AirPrint?
• A volume slider control in the Multitaskbar
• New icon for Voice Memos
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Anything else?

UPDATE: There’s a trick to use the Find my iPhone in a 3GS or similar. I found out that if you create everything from an iPhone 4 (and/or presumably an iPod TOuch latest gen), you can later go to your 3Gs and enter the same data and it will work. :)