I have Line A and Line B. Line B is currently on the iPhone. Line A currently doesn't have a phone using it. I want to cancel Line B and use Line A on the iPhone. Can this be done right over the phone, without any sim card being mailed to me or anything?
You have a DEVICE question, ask here or Apple.
You have a SERVICE question, get on the AT&T forums or call AT&T.
Don't bump - it's frowned upon in the rules.