Just a quick fix for people who are experiencing that all of the sudden, without any warning, they can’t start their downloaded apps on their iPhone.

Here is what happens:
– you click on app
– app starts loading
– title screen for app is shown
– app doesn’t start but you end up on the Home screen

Here is the fix:
1. delete a free app that you may have on your phone (NOTE: it must be an app downloaded from AppStore – I don’t think apps from downloaded from Cydia or Rock will work).
2. download and install a free app from AppStore
3. launch the app you downloaded in step 2
4. try launching any other app that didn’t work before

You can try skipping step 1 above if you want.

I think that this problem only occurs on jailbroken iPhones and/or ones with pirated apps on it. Anyhoop, this fix worked on my jailbroken (but not SIM unlocked) 3G phone with OS 3.1.2.