sync Thunderbird address book with IPad

Its possible that bell south does not support calendar sync - i do not know the system at all

I believe you may be using a new AT&T/Yahoo platform. I'm not sure if the new system supports contact sync
And the imap settings are
youremail@bellsouth.net
Incoming (IMAP) imap.mail.yahoo.com
Outgoing (SMTP) smtp.att.yahoo.com
Select SSL

BUT what I do with email systems that do not support sync of calendar or contacts , is to use a 2nd email account which will. I use microsofts outlook.com / hotmail.com emal
and then set that up on thunderbird and on ipad/iphone

now the email will still be via bellsouth but the contacts & calendar sync via the outlook.com email , and just ignore any emails via that system