A lot of people are having difficulty with the reception on their iPhone 4. This is due to a technical error in Apple’s design.
If you are having issues with your reception you can request a case or armband from Apple that fixes the problem rather easily, simply fix the case to your iPhone and you’re ready to go.
You can go to the Apple website (http://store.apple.com/uk/browse/home/shop_iphone/iphone_accessories/cases) and request a free case or a refund for anyone that’s already purchased one.