Determine device (iPhone, iPod Touch) with iOS

You can use the UIDevice class like this:

NSString *deviceType = [UIDevice currentDevice].model;

if([deviceType isEqualToString:@"iPhone"])
    // it's an iPhone

This is an update for UIDeviceHardware.m from the answer above.

- (NSString *)platformString
{
    NSString *platform = [self platform];

    if ([platform isEqualToString:@"iPhone1,1"])    return @"iPhone 1G";
    if ([platform isEqualToString:@"iPhone1,2"])    return @"iPhone 3G";
    if ([platform isEqualToString:@"iPhone2,1"])    return @"iPhone 3GS";
    if ([platform isEqualToString:@"iPhone3,1"])    return @"iPhone 4";
    if ([platform isEqualToString:@"iPhone3,3"])    return @"Verizon iPhone 4";
    if ([platform isEqualToString:@"iPhone4,1"])    return @"iPhone 4S";
    if ([platform isEqualToString:@"iPhone5,1"])    return @"iPhone 5 (GSM)";
    if ([platform isEqualToString:@"iPhone5,2"])    return @"iPhone 5 (GSM+CDMA)";
    if ([platform isEqualToString:@"iPhone5,3"])    return @"iPhone 5c (GSM)";
    if ([platform isEqualToString:@"iPhone5,4"])    return @"iPhone 5c (GSM+CDMA)";
    if ([platform isEqualToString:@"iPhone6,1"])    return @"iPhone 5s (GSM)";
    if ([platform isEqualToString:@"iPhone6,2"])    return @"iPhone 5s (GSM+CDMA)";
    if ([platform isEqualToString:@"iPhone7,1"])    return @"iPhone 6";
    if ([platform isEqualToString:@"iPhone7,2"])    return @"iPhone 6 Plus";
    if ([platform isEqualToString:@"iPhone8,1"])    return @"iPhone 6s";
    if ([platform isEqualToString:@"iPhone8,2"])    return @"iPhone 6s Plus";
    if ([platform isEqualToString:@"iPhone8,4"])    return @"iPhone SE";
    if ([platform isEqualToString:@"iPod1,1"])      return @"iPod Touch 1G";
    if ([platform isEqualToString:@"iPod2,1"])      return @"iPod Touch 2G";
    if ([platform isEqualToString:@"iPod3,1"])      return @"iPod Touch 3G";
    if ([platform isEqualToString:@"iPod4,1"])      return @"iPod Touch 4G";
    if ([platform isEqualToString:@"iPod5,1"])      return @"iPod Touch 5G";
    if ([platform isEqualToString:@"iPod7,1"])      return @"iPod Touch 6G";
    if ([platform isEqualToString:@"iPad1,1"])      return @"iPad";
    if ([platform isEqualToString:@"iPad2,1"])      return @"iPad 2 (WiFi)";
    if ([platform isEqualToString:@"iPad2,2"])      return @"iPad 2 (GSM)";
    if ([platform isEqualToString:@"iPad2,3"])      return @"iPad 2 (CDMA)";
    if ([platform isEqualToString:@"iPad2,4"])      return @"iPad 2 (WiFi)";
    if ([platform isEqualToString:@"iPad2,5"])      return @"iPad Mini (WiFi)";
    if ([platform isEqualToString:@"iPad2,6"])      return @"iPad Mini (GSM)";
    if ([platform isEqualToString:@"iPad2,7"])      return @"iPad Mini (GSM+CDMA)";
    if ([platform isEqualToString:@"iPad3,1"])      return @"iPad 3 (WiFi)";
    if ([platform isEqualToString:@"iPad3,2"])      return @"iPad 3 (GSM+CDMA)";
    if ([platform isEqualToString:@"iPad3,3"])      return @"iPad 3 (GSM)";
    if ([platform isEqualToString:@"iPad3,4"])      return @"iPad 4 (WiFi)";
    if ([platform isEqualToString:@"iPad3,5"])      return @"iPad 4 (GSM)";
    if ([platform isEqualToString:@"iPad3,6"])      return @"iPad 4 (GSM+CDMA)";
    if ([platform isEqualToString:@"iPad4,1"])      return @"iPad Air (WiFi)";
    if ([platform isEqualToString:@"iPad4,2"])      return @"iPad Air (Cellular)";
    if ([platform isEqualToString:@"iPad4,4"])      return @"iPad mini 2G (WiFi)";
    if ([platform isEqualToString:@"iPad4,5"])      return @"iPad mini 2G (Cellular)";
    if ([platform isEqualToString:@"iPad5,1"])      return @"iPad mini 4 (WiFi)";
    if ([platform isEqualToString:@"iPad5,2"])      return @"iPad mini 4 (Cellular)";
    if ([platform isEqualToString:@"iPad5,3"])      return @"iPad Air 2 (WiFi)";
    if ([platform isEqualToString:@"iPad5,4"])      return @"iPad Air 2 (Cellular)";
    if ([platform isEqualToString:@"iPad6,3"])      return @"iPad Pro 9.7 inch (WiFi)";
    if ([platform isEqualToString:@"iPad6,4"])      return @"iPad Pro 9.7 inch (Cellular)";
    if ([platform isEqualToString:@"iPad6,7"])      return @"iPad Pro 12.9 inch (WiFi)";
    if ([platform isEqualToString:@"iPad6,8"])      return @"iPad Pro 12.9 inch (Cellular)";
    if ([platform isEqualToString:@"i386"])         return @"Simulator";
    if ([platform isEqualToString:@"x86_64"])       return @"Simulator";

    return platform;
}

Please feel free to use this class (gist @ github)

CODE REMOVED AND RELOCATED TO

https://gist.github.com/1323251

UPDATE (01/14/11)

Obviously, this code is a bit out of date by now, but it can certainly be updated using the code on this thread provided by Brian Robbins which includes similar code with updated models. Thanks for the support on this thread.