There should be a number, which adds the last caller to the black-list (list of blocked numbers). This number can be complicated, to ensure that it isn't dialed by mistake.
This would add the last dialed number to the black-list, minus X digits. Therefore, **6699#3388**0 would add the complete number, while **6699#3388**3 would add the last caller minus three digits.
This number could then be put in the telephone's phone book (**6699#3388**1) for easy access under "block last caller", where it couldn't be dialed by mistake.
I think that this would be a nifty feature, considering that unwanted calls (robot calls) have become a pestilence everywhere.