if ( [[[UIDevice currentDevice] systemVersion] doubleValue ] >= 4.0 )
    {
        MFMessageComposeViewController *controller = [[MFMessageComposeViewController alloc] init];
        if([MFMessageComposeViewController canSendText])
        {
            controller.body = str;
            controller.recipients = nil;
            controller.messageComposeDelegate = self;
            [self presentViewController:controller animated:YES completion:nil];
        }
    }