Backing up address book to cloud

Here is the tutorial and information.  https://www.att.com/att/addressbook/desktop/en/index.html#tab3

I strongly suggest you designate another default for your contacts.  If you leave ATT service, the cloud and ATT address book is immediately unavailable to you and you can't retrieve anything.  We get upset posts from customers who switched to other carriers and lost contacts and personal photos.

So I guess the answer to my first question is YES.  

So I went to the tutorial to try to set up the ATT Address Book.  I determined that my phone is compatible.  However, when I go to the Address Book menu, anything requiring communication says I don't have a cellular connection.  Yet, in settings, I have cellular data turned on and I even tried turning on data roaming to see if that made a difference; it didn't.  I am home and able to use my phone and it shows several bars of signal.

Any suggestions?  Thanks

Actually, I solved the communication error  problem myself:   You apprently have to shut off WIFI in order to force the phone to use cellular data.  OK, so it synched.

However, the other question from my original post is still an issue -- I cannot sign up to register the address book because it won't recognize my GoPhone number and PIN as a valid ID.

You have to register first.  Just like ATT messages, it uses a user name and password, not your current account login.

Thanks.