After following the excellent documentation by Stephen Blackheath, I was able to setup a new project with GHC support in no time.

The simplest iPhone program that compiles looks like this

main.m

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#import <UIKit/UIKit.h>

extern int Haskell_main(int argc, char* argv[]);

int main(int argc, char *argv[]) {
  Haskell_main(argc, argv);
}

int kon(void) {
  NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
  int retVal = UIApplicationMain(0, nil, nil, nil);
  [pool release];
  return retVal;
}

Main.hs

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{-# LANGUAGE ForeignFunctionInterface #-}

import Foreign.C.Types

foreign import ccall safe "kon" kon :: IO CInt

main = kon

main.m calls into haskell's Main.hs, and haskell calls back via FFI a function that init the UiKit.