DisplayMetrics does not function on HTC WildFire?

Question

I use the following code to see whether the code runs on a small screen. This works fine in the emulator. However when the code runs on a HTC WildFire it fails.

    DisplayMetrics dm = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(dm);

    if (dm.heightPixels==320 && dm.widthPixels==240){
        /* Here code for small screens */
    }

Does anyone has an idea why??

Thanks in advance Jasper