1. A method of operating an electronic device comprising the steps of: initiating entry of a content string by receiving a first key selection input, said first key corresponding to a first set of more than one textual characters; determining a most probable completion alternative using a personalized and learning database, said completion alternative being either (a) a most probable character selected from said first set of more than one textual characters or (b) a most probable sub-string, said sub-string beginning with said most probable character and including at least one additional character; displaying the most probable completion alternative in a content string entry line of a display of said electronic device; receiving a second input, said second input being either a second key corresponding to a second set of more than one textual characters or a selection key; and adding the most probable completion alternative to the content string entry line of said display for said second input being said selection key and said most probable completion alternative being the most probable sub-string, and adding a second completion alternative for said second input being said second key, said second completion alternative being a most probable second sub-string, said second sub-string beginning with said most probable first character and including said most probable second character and at least a most probable third character; wherein a user interface is provided that comprises a navigation key having a first set of controls, said first set of controls in an editing mode, for acceptance or non-acceptance of the most probable completion alternative currently displayed at the display and a second set of controls, said second set of controls in the editing mode, for changing or overriding the most probable completion alternative currently displayed at the display; wherein said first of controls are configured for scrolling a cursor right one character at a time or scrolling the cursor left one character at a time when said first set of controls are in a navigation mode; wherein said second set of controls are configured for scrolling the cursor down one line at a time or scrolling the cursor up one line at a time, when said second set of controls are in the navigation mode; and wherein: a right control of said first set of controls is configured for, in navigation mode and in a hold and press mode, jumping the cursor to the right one word at a time; a left control of said first set of controls is configured for, in navigation mode and in the hold and press mode, jumping the cursor left one word at a time; the left control being further configured for, in editing mode and in the hold and press mode, dismissing prediction and locking a last key press entry.