My iPhone won't download certain free apps
Go to your iTunes account, manage your hidden and downloadable apps and unhide the app you want to download again.


Open iTunes
Select 'Store' menu option --> 'View Account'
Look in section iTunes in the Cloud
Look for subsection 'Hidden Purchases'
Click on the 'Manage' link
Press the 'Apps' button
Find the App you are trying to download from the list
Click 'Unhide'


You can now download app from App Store on your iPhone.