isGameCenterAvailable.m

/**
 * Determines if the device running this
 * application is Game Center ready.
 *
 * @return true if Game Center is available.
 */
BOOL isGameCenterAvailable();



#import <sys/utsname.h>

BOOL isGameCenterAvailable()
{
    // Check for presence of GKLocalPlayer API.
    Class gcClass = (NSClassFromString(@"GKLocalPlayer"));
    
    // The device must be running running iOS 4.1 or later.
    NSString *reqSysVer = @"4.1";
    NSString *currSysVer = [[UIDevice currentDevice] systemVersion];
    BOOL osVersionSupported = ([currSysVer compare:reqSysVer options:NSNumericSearch] != NSOrderedAscending);
    
    // 1st Gen iPod and 3G don't support Game Center
    struct utsname systemInfo;
    uname(&systemInfo);
    NSString *theModel = [NSString stringWithCString:systemInfo.machine encoding:NSUTF8StringEncoding];
    if ([theModel isEqualToString:@"iPhone1,2"] ||
        [theModel isEqualToString:@"iPod1,1"])
    {
        return FALSE;
    }
    
    return (gcClass && osVersionSupported);
}

Thanks for sharing!