I dont have iphone 5 but on the other phone this code worked great:
NSMutableDictionary *devices = [[NSMutableDictionary alloc] init];
[devices setObject:@"simulator"                     forKey:@"i386"];
[devices setObject:@"iPod Touch"                    forKey:@"iPod1,1"];
[devices setObject:@"iPod Touch Second Generation"  forKey:@"iPod2,1"];
[devices setObject:@"iPod Touch Third Generation"   forKey:@"iPod3,1"];
[devices setObject:@"iPod Touch Fourth Generation"  forKey:@"iPod4,1"];
[devices setObject:@"iPhone"                        forKey:@"iPhone1,1"];
[devices setObject:@"iPhone 3G"                     forKey:@"iPhone1,2"];
[devices setObject:@"iPhone 3GS"                    forKey:@"iPhone2,1"];
[devices setObject:@"iPad"                          forKey:@"iPad1,1"];
[devices setObject:@"iPad 2"                        forKey:@"iPad2,1"];
[devices setObject:@"iPhone 4"                      forKey:@"iPhone3,1"];
[devices setObject:@"iPhone 4S"                     forKey:@"iPhone4"];
[devices setObject:@"iPhone 5"                      forKey:@"iPhone5"];
- (NSString *) getDeviceModel
{
    struct utsname systemInfo;
    uname(&systemInfo);
    return [devices objectForKey:[NSString stringWithCString:systemInfo.machine encoding:NSUTF8StringEncoding]];
}
Remember to import:
#import "sys/utsname.h"