why can i add files to my ipod but not my iphone?
In order to be able to drag/drop media tracks freely from your iTunes library to your iPhone, you need to set your iTunes sync settings for your iPhone to manual mode.


Connect your iPhone to your computer and run iTunes. 
Select your iPhone, iPad, or iPod. If your device is not visible in the upper right corner of the screen, choose Library first.
Click the Summary tab and select "Manually manage music and videos". 
Make sure that contacts and calendar sync is not enabled from the Info tab
Click Apply. 


You can now drag/drop songs from your iTunes library to your iPhone