iPhone still sleeping with the proper API calls

Question

On Init, I call:

[[UIApplication sharedApplication] setIdleTimerDisabled:YES];

My 3GS will never goto sleep while unplugged, but my 3G will. Any ideas? Rebooting will sometimes fix the issue, but it just crops up again.. Both phones have the latest OS.

I've even tried putting that on a 1sec NSTimer, still nothing. The screen will dim, and eventually just sleep.

Thanks for reading!