iOS Development: How can I induce low memory warnings on device?
You can call the private method:
[[UIApplication sharedApplication] performSelector:@selector(_performMemoryWarning)];
Just remember to use it on debug only, or else your app will get rejected.
The iOS Simulator's Simulate Memory Warning menu item allows you to simulate a memory warning.
Using Instruments, use the menu item: Instrument -> Simulate Memory Warning.
To use Instruments on your app from Xcode, use the Product -> Profile menu item.