This never happened with my 3G but ever since I upgraded to the 3GS.....it happens.
When I turn on the iPhone, it is at the correct brightness.
When I slide to unlock, the brightness diminishes where upon the brightness will suddenly come back to normal after a few moments of use.
When I turn on the iPhone, it is at the correct brightness.
When I slide to unlock, the brightness diminishes where upon the brightness will suddenly come back to normal after a few moments of use.