Actually, you'll want your URL to start with itms-appss:
if you want it to open in the App Store app, where someone would actually gift an app. This feels more natural than Safari popping up.
// example app id for batman arkham city lockdown
#define APP_ID 459850726
NSString *GiftAppURL = [NSString stringWithFormat:@"itms-appss://buy.itunes.apple.com/WebObjects/MZFinance.woa/wa/giftSongsWizard?gift=1&salableAdamId=%d&productType=C&pricingParameter=STDQ&mt=8&ign-mscache=1",
APP_ID];
[[UIApplication sharedApplication] openURL:[NSURL URLWithString:GiftAppURL]];
APP_ID should obviously be defined to the Apple ID of your app.
Also worth noting, the URL is case sensitive.