"Line Out" on iPhone dock - safe to plug in external speakers?

Hi Everyone,

Just wondering if anyone has any experience using external speakers connected to the line out jack on the iphone dock? My concern is whether or not doing this will affect the power system of the iphone in any way. I have heard stories of people docking their iphones into hifi docks (such as Apple hifi and bose sound dock) and after a few minutes their iphones heat up like an oven and then die (logic board overheats and fails). I know I never want to test that out, but I'm just curious if anyone has experienced or heard of anyone "frying" their iphone by plugging in external speakers into the line out on the dock.....thanks in advance for your thoughts.