Bring up keyboard when button is pressed

I have imported captured screen and reformatted.

There is a field in the screen where text is to be input.

The keyboard is set to "hide" so the keyboard would not pop up.

3 buttons have been created,

1.Button "A" (which will enter A+ENTER)

2.Button "B"(which will enter B+ENTER)

3.Button "Other" I want this button to bring up the keyboard.

The keyboard is hidden by default. The user will select "A" or "B" but if user want different option the user should be able to press the "Other" button and then the keyboard would pop up and the user will be able to enter custom text.