Here's how to hard reset the Google Nexus S 4G also known as Samsung SPH-D720. This will restore the phone data to original factory default settings. This help fix if the phone experience several error problem like frozen or unresponsive.
Please note: Make a back up copy of all your personal data first, before proceeding. The result of this procedure will delete all data from the Google Nexus S 4G.
1. On the main home screen, select menu
2. Tap Settings, then Privacy
3. Select Factory data reset
4. Select Reset phone
5. Enter the password if prompted, then confirm by tapping Erase everything
1. Turn the power off. Take the battery out from the phone and reinsert it back again
2. Hold the Volume Down button
3. Press and release the Power button
4. You are now presented with a menu that allows for Fastbook, Recovery, Clear Storage, and Simlock
5. Select Clear Storage by pressing the Volume Down button
6. Press and release the Power button
7. Confirm by selecting: Volume Up for YES and Volume Down for NO
Once the wipe is complete, the phone will reboot to its factory fresh state.