iOS 4.2.1 is the latest version that will run on an iPhone 3G.
If the developers of the apps you wish to use no longer support 4.2.1,
you will have to get a newer iPhone that runs a version of iOS supported
by the apps you wish to use.
Which versions on iOS that are supported by an app is a decision made
by the developer of the app and not by Apple.
I still have an old 3G which I use mostly as a ipod/radio. By accident I found you can overide the i-tunes block.
1. Select Apps in Apps store icon on the phone.
2. Choose App to download
3. At "Instal" button press it QUICKLY in blocks of 3 presses, keep doing this until it overides the i-tune warning, then if there were legacy versions for os 4.2.1 it says something like "this app is for os 5 or above", but gives you a choice to download an older version. Select this.
Sometimes it says the Apps is for newer hardware, requiring motion sensors, front camera's etc.. just got to accept these ones don't work on legacy hardware.
4. Download does not work for all Apps, esp. newer ones written after os 4.21 or if the developer doesn't have the vintage apps archived- e.g. Instagram downloads, but won't run (wants to update), or WSJ and Barrons stalls and goes through a download loop.
I am not making this up, as I bought this old 3g unit on e-bay, after a complete factory reset I now have:
- Tune-in, FB, Pandora,Skype, Twitter, Bloomberg, MSNBC, Forbes, Marketwatch, Viber, amongst a host of other news apps like LATimes.
Some Apps will download ok, and then at activation says its too old and no longer supported e.g Whats App.
Otherwise, good luck. Tune-in, Pandora, Skype and Twitter is all I need to keep me happy with an old unit, even though I've got newer hardware. Never let anything die unnaturally.