The volume buttons on a few rare devices were found to be reversed. The signs on a few volume buttons changed so when you press ‘+’ the volume reduced and when you press ‘-‘ the volume increases. This is a small hiccup but it can be unwanted for users who get stuck with a phone like this.
Take the device to Apple and the customer service team will be happy to make a replacement while the phone is in warranty. If your phone’s warranty has ended, then you can take it to third-party technicians who can reverse the buttons for you.
Other common iPhone 4 problems include Wi-Fi issues, Bluetooth connectivity problems, email issues, battery problems, and some even reported that the glass could easily get scratched and broken.