Is there a unique Android device ID?

The following code returns the device serial number using a hidden Android API. But, this code don't works on Samsung Galaxy Tab because "ro.serialno" isn't set on this device.

String serial = null;

try {
    Class<?> c = Class.forName("android.os.SystemProperties");
    Method get = c.getMethod("get", String.class);
    serial = (String) get.invoke(c, "ro.serialno");
}
catch (Exception ignored) {

}

A Serial field was added to the Build class in API level 9 (Android 2.3 - Gingerbread). Documentation says it represents the hardware serial number. Thus it should be unique, if it exists on the device.

I don't know whether it is actually supported (=not null) by all devices with API level >= 9 though.

How about the IMEI. That is unique for Android or other mobile devices.

Here is how I am generating the unique id:

public static String getDeviceId(Context ctx)
{
    TelephonyManager tm = (TelephonyManager) ctx.getSystemService(Context.TELEPHONY_SERVICE);

    String tmDevice = tm.getDeviceId();
    String androidId = Secure.getString(ctx.getContentResolver(), Secure.ANDROID_ID);
    String serial = null;
    if(Build.VERSION.SDK_INT > Build.VERSION_CODES.FROYO) serial = Build.SERIAL;

    if(tmDevice != null) return "01" + tmDevice;
    if(androidId != null) return "02" + androidId;
    if(serial != null) return "03" + serial;
    // other alternatives (i.e. Wi-Fi MAC, Bluetooth MAC, etc.)

    return null;
}

I use the following code to get the IMEI or use Secure.ANDROID_ID as an alternative, when the device doesn't have phone capabilities:

String identifier = null;
TelephonyManager tm = (TelephonyManager)context.getSystemService(Context.TELEPHONY_SERVICE));
if (tm != null)
      identifier = tm.getDeviceId();
if (identifier == null || identifier .length() == 0)
      identifier = Secure.getString(activity.getContentResolver(),Secure.ANDROID_ID);