Why is there always a dot on the 5 key of a phone?

Question

Why is there always a dot on the 5 key of a phone?

Answer 1

so that blinds and people with poor visibility can identify the buttons easily this key is in the centre of the centre line  

Answer 2

I believe it is so that blind people know where the buttons are.

Answer 3

This is an old but always was a good idea.  Contrary to popular belief this was never truly created to help the blind but to rather help all users dial without looking at the keypad.  Because the dot is located on the 5 key (which is always the center of the keypad) it is easy to locate all of the other number keys.