A category on UIApplication for determining the iPhone device

UIApplication+iPhoneVersion.h

#import <UIKit/UIKit.h>

#define IS_IPHONE (!IS_IPAD)
#define IS_IPAD (UI_USER_INTERFACE_IDIOM() != UIUserInterfaceIdiomPhone)

/**
 Provides a few methods to determine what sort of device the application is
 running on. Specifically, the methods make it easy to determine what sort of
 iPhone resolution is available: `[[UIApplication sharedApplication] isIphone3]`
 */
@interface UIApplication (iPhoneVersion)
/** Returns YES if the device is only capable of 320x480. */
- (BOOL)isIphone3;

/** Returns YES if the device's native resolution is 640x960. */
- (BOOL)isIphone4;

/**
 Returns YES if the devices's native resolution is 640x1136. Well, not quite.
 Even if the native resolution is 640x1136, this method will only return YES
 if a Default-568h@2x.png has been added to the project.
 */
- (BOOL)isIphone5;
@end

UIApplication+iPhoneVersion.m

#import "UIApplication+iPhoneVersion.h"

@implementation UIApplication (iPhoneVersion)
/**
 A private function to reduce some typing.
 */
static bool screenMatchesSize(int x, int y) {
  return CGSizeEqualToSize([[UIScreen mainScreen] preferredMode].size,
                           CGSizeMake(x, y));
}

/**
 A private function to reduce redundancy.
 */
static bool isPhoneVersion(int phoneVersion) {
  if (!IS_IPHONE) {
    return NO;
  }
  
  BOOL result = NO;
  
  switch (phoneVersion) {
    case 3:
      result = screenMatchesSize(320, 480);
      break;
    
    case 4:
      result = screenMatchesSize(640, 960);
      break;
    
    case 5:
      result = screenMatchesSize(640, 1136);
      break;
      
    default:
      break;
  }
  
  return result;
}

- (BOOL)isIphone3
{
  return isPhoneVersion(3);
}

- (BOOL)isIphone4
{
  return isPhoneVersion(4);
}

- (BOOL)isIphone5
{
  return isPhoneVersion(5);
}
@end