I got the greek version of the phone.
It has a builtin hard reset function which is activated as follows:
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
I took the above from a post on XDA Devs, and it WORKS on a greek-localized Samsung i780.
It is possible that other versions use different bootloaders, which do not have support for this combo