Nokia Diagnostics is a free utility that can help you troubleshoot and resolve common problems with your Nokia phones.
For instance, when you need to configure your Nokia device on a different Internet Connection (like moving from one Wi-Fi network to another), Nokia Diagnostics can automatically identify the right Internet settings for you.
The utility can also help you test the phone’s battery charger, the loudspeaker and even the earpiece.
Nokia Diagnostics works with all S60 5th edition devices (like the N-series, Nokia 5800, etc.) while support for 3rd edition devices is expected soon.
Related: Test your BlackBerry Phone for Problems