I think what iham wants is the kind of keypad entry you get with Mobile phone texting...

ie.. Button '2' is also A B or C...

So you press it once you get '2', you press it again within say 1 second, you get 'A', press again and you get 'B', and again you get 'C'... then back to '2' again, and so on. If you leave it more than 1 second, it remains with whatever the last selection was and moves to the next character position.

This really means integrating the Keypad with a Display... because you will be changing the displayed value depending if the same key is pressed again within the timeout period, and having an Array for storing the resultant Alphanumeric Text 'string'.