After a deep investigation on the internet I must say that the Nokia Lumia 520 is a great choice for a budget smart phone for mobile gaming. It has an decent GPU compared to other budget phones. Most of the budget phones I checked had an Adreno 203 GPU, while the Nokia Lumia 520 had an Adreno 305 GPU which is way better. I was looking for an Andorid phone but I realized that Windows Phone 8 is an advantage for mobile gaming since It is a very light and fast OS. And all this comes in a very affordable price that you won't find in any other 4" inch budget phone.