非常简单的解决方法

if(UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone)
{
    CGSize result = [[UIScreen mainScreen] bounds].size;
    if(result.height == 480)
    {
        // iPhone Classic
    }
    if(result.height == 568)
    {
        // iPhone 5
    }
}

我们现在需要考虑iPhone 6和6Plus的屏幕尺寸。以下是最新的答案

if(UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone)
{
    //its iPhone. Find out which one?

    CGSize result = [[UIScreen mainScreen] bounds].size;
    if(result.height == 480)
    {
        // iPhone Classic
    }
    else if(result.height == 568)
    {
        // iPhone 5
    }
    else if(result.height == 667)
    {
        // iPhone 6
    }
   else if(result.height == 736)
    {
        // iPhone 6 Plus
    }
}
else
{
     //its iPad
}

一些有用的信息

iPhone 6 Plus   736x414 points  2208x1242 pixels    3x scale    1920x1080 physical pixels   401 physical ppi    5.5"
iPhone 6        667x375 points  1334x750 pixels     2x scale    1334x750 physical pixels    326 physical ppi    4.7"
iPhone 5        568x320 points  1136x640 pixels     2x scale    1136x640 physical pixels    326 physical ppi    4.0"
iPhone 4        480x320 points  960x640 pixels      2x scale    960x640 physical pixels     326 physical ppi    3.5"
iPhone 3GS      480x320 points  480x320 pixels      1x scale    480x320 physical pixels     163 physical ppi    3.5"

依赖规模在很多层面上都是错误的。如果我们问系统呢?

- (NSString *) getDeviceModel
{
    struct utsname systemInfo;
    uname(&systemInfo);
    return [NSString stringWithCString:systemInfo.machine encoding:NSUTF8StringEncoding];
}

摘自《检测硬件类型的最佳方法，iPhone4还是iPhone5?》edzio27回答。

这里是正确的测试设备，不依赖于方向

- (BOOL)isIPhone5
{
    CGSize size = [[UIScreen mainScreen] bounds].size;
    if (MIN(size.width,size.height) == 320 && MAX(size.width,size.height == 568)) {
        return YES;
    }
    return NO;
}

非常简单的解决方法

if(UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone)
{
    CGSize result = [[UIScreen mainScreen] bounds].size;
    if(result.height == 480)
    {
        // iPhone Classic
    }
    if(result.height == 568)
    {
        // iPhone 5
    }
}

+(BOOL)isDeviceiPhone5
{
    BOOL iPhone5 = FALSE;

    CGRect screenBounds = [[UIScreen mainScreen] bounds];
    if (screenBounds.size.height == 568)
    {
        // code for 4-inch screen
        iPhone5 = TRUE;
    }
    else
    {
        iPhone5 = FALSE;
        // code for 3.5-inch screen
    }
    return iPhone5;

}