iPhone 3GS blanks out and crashes open Application every few minutes (30 second to 2 minute intervals). Apps are still “open” in the Fast-Switch dock, but have been minimized by the crash. The crashes occur regardless of the App that is open, and prevails when Settings App is open.
Symptoms will not subside despite soft-reboots and hard-reboots.
This specific problem will occur if you have an iPhone 3GS running iOS 5 with an iCloud account linked and operational on the device.
Cause: iCloud. Specific cause undetermined; likely to be an unresolvable sync error.
Connect your iPhone to your computer and back it up.
On your iPhone, go to Settings > Mail, Contacts, Calendars > iCloud > Delete Account.
Click “Delete” to confirm the removal of iCloud data from the iPhone.
When complete, add your iCloud account back by going to Settings > Mail, Contacts, Calendars > Add Account.
Disclaimer: I am not responsible for any direct or indirect data loss as a result of using this solution. Remember to back-up first.