In order to hard reset a Siemens SX66, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Siemens SX66 device will be brought back to the default configuration of a brand new device.
1. Prepare the phone's stylus. Turn off the phone.
2. Now press'n'hold the Power button.
3. Pick up the Stylus and, while holding Power button, insert it into the reset button hole.
4. Phone should now restart'n'reboot.