1. Power off the phone
2. Hold down the begin call and end call buttons (green & red)
3. Press and hold the power button
4. Once the phone's status LED turns red, RELEASE the power button but KEEP the other 2 pushed
5. You will get a prompt to press the space key to format, or any other key to continue


It is possible that other versions use different bootloaders, which do not have support for this steps.., nor you can only do for FULL reset *2767*3855#



you can do this for HANG-up matters...