Sounds like to me either you don't have active SIM card in new phone, or else you need to pull old SIM card from old phone an shut it off. Then restart new phone. If that still doesn't work then it may be a faulty port. Happens sometimes an the rep may have to redo the port. Takes like 5 minutes.
I would talk to AT&T for that question. This is Google contribute. I'm a customer just like you. Sorry.
Thanks! Your answer is awaiting moderation.