I am getting longitude=0.0 and latitude=0.0 on tablet while this is working perfectly on the phone. 
I am using LocationManager.NETWORK_PROVIDER and not the GPS_PROVIDER so what could be the cause please?
Logcat output??
that's my code:
 // Acquire a reference to the system Location Manager
         locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
     // Define a listener that responds to location updates
     locationListener = new LocationListener() {
         public void onLocationChanged(Location location) {
           // Called when a new location is found by the network location provider.
           longitude=location.getLongitude();
           latitude=location.getLatitude();
         }
         public void onStatusChanged(String provider, int status, Bundle extras) {}
         public void onProviderEnabled(String provider) {}
         public void onProviderDisabled(String provider) {}
       };
     //Or use LocationManager.GPS_PROVIDER
     String locationProvider = LocationManager.NETWORK_PROVIDER;
     // Register the listener with the Location Manager to receive location updates
     locationManager.requestLocationUpdates(locationProvider, 0, 0, locationListener);
     Location lastKnownLocation = locationManager.getLastKnownLocation(locationProvider);
     if(lastKnownLocation!=null){
         longitude=lastKnownLocation.getLongitude();
         latitude=lastKnownLocation.getLatitude();
     }
 
                        
Check out Location settings inside your device settings. This seems not a problem with your code, but your device settings. In my Ginger bread, it's as:
Settings -> Location&security -> Use wireless networks