UIDeviceHardware.h

//
//  UIDeviceHardware.h
//
//  Used to determine EXACT version of device software is running on.

#import <Foundation/Foundation.h>

@interface UIDeviceHardware : NSObject 

- (NSString *) platform;
- (NSString *) platformString;

@end

UIDeviceHardware.m

//
//  UIDeviceHardware.m
//
//  Used to determine EXACT version of device software is running on.

#import "UIDeviceHardware.h"
#include <sys/types.h>
#include <sys/sysctl.h>

@implementation UIDeviceHardware

- (NSString *) platform{
    size_t size;
    sysctlbyname("hw.machine", NULL, &size, NULL, 0);
    char *machine = malloc(size);
    sysctlbyname("hw.machine", machine, &size, NULL, 0);
    NSString *platform = [NSString stringWithUTF8String:machine];
    free(machine);
    return platform;
}

- (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:@"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:@"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:@"i386"])         return @"Simulator";
if ([platform isEqualToString:@"x86_64"])       return @"Simulator";
    return platform;
}

@end

usage.txt

UIDeviceHardware *h=[[UIDeviceHardware alloc] init];
[self setDeviceModel:[h platformString]];   
[h release];

Nice code! I use SDiPhoneVersion to check that.