iPhone Assign function to hardware button

[Planins]

I want to assign a letter or the backspace to a hardware button like the volume key, I think I have seen such tweaks in Cydia, at least to assign another functions to the volume rockers. Thanks for your answers

 

[Applejuiced]

Use activator.
It has many options for keys, gestures, double tap, long hold, triple click etc...
Not sure if you can assign a letter but you can assign other functions or programs.