You get Warhawk free with the Starhawk Online Network pass, Sony has revealed.
Sony Computer Entertainment Europe has worked behind the scenes emulating the PSone version of Warhawk, released in 1995, and now it's ready for the launch of PlayStation 3 exclusive Starhawk.
To get it you need to redeem the Starhawk Online Network pass found on the back of the Starhawk manual. Warhawk will then pop up in your download list.
PSone Classics currently do not work with PS Vita, although Sony has indicated that they will be enabled in the near future.