I recently upgraded operating system of my iPhone 3G to iOS 4. iPhone 3G is already slow and sluggish. For a smartphone that has been introduced hardly 2 years ago, 128 MB of memory is so small. My fridge has more memory than that! Now with iOS 4, it is even slower. Maps and Calendar applications are slow to the point of being unusable. I lunch Maps application and I have to wait quite a few seconds for map to load. It may be just a few seconds but believe me, when you are on the go and in rush, even that feels like eternity. I will try to downgrade to iPhone OS 3. And right now, I am not sure if my next smartphone is an iPhone. Android-based phones look tempting.