HT2458 Why did AT&T add password to voicemail

For no reason known to a seasoned iPhone user, as I setup my new iPhone 5, a popup asked for my voicemail password!  I have never had a voicemail password and had no idea what it was, so I entered some numbers that might be the one, but  iPhone just kept asking for this.  Never did it tell me it was wrong or Try again.  I finally called AT&T and they reset the PW and I should change it.  But WHY???? Is there any need for this to be different than the iPhone 4 or 4S, with all the added frustration. 

Maybe there is a logical reason for such a password, as it allows one to get voice messages from any phone.  Maybe this service has value, but might that be better served with an OPT IN or OPT OUT question during the setup rather than the confusion with a one answer dialog box.

Comment welcome!