Why won't my apps work on iPhone 3G?

[Andrew]

I need more info...

Is it jailbroken?
Do these apps have known bugs?

...if not, my only answers would be to...

Option 1: Refresh the phone: (This doesn't lose any data or change any person settings. It's just supposed to fix your issue.)

Hold down both the home and sleep/wake buttons (2 buttons) until your screen goes blank, then, turn your phone back on with the sleep wake button after the phone has went blank. THis may take longer than a typical startup, be patient.

Option 2: Reset the phone: (This will change only your phones settings which can be switched back easily
....
ex. wifi networks, location warnings, notifications, etc. This will not affect your home screen layout or anything else.)

Open Settings. Then tap General>Reset>Reset All Settings

Option 3: Restore (This method will keep everything intact if done properly.)

First, back up your phone to iTunes (under your phones tab to the left in iTunes, right click it and click the option "Back Up" or something along those lines).

After the back is COMPLETE, under your phone summary, click restore.

Once everything has finished, try opening the Apps on your phone, if they don't work....

Option 5: New iPhone

Unfortunately, many apps available on the app store today have various issues with older generation hardware.

I hope this helps, and good luck.