My main email is through att. I set up my droid to receive and send email from that att account. I can receive email from the att account but can not reply to that mail. So I set up a gmail account on my phone. At that point, I have no idea how to retrieve my contacts from my Macbook, and would welcome technical help here.
Set up your AT&T account as a POP3 account through Gmail. In settings go to your accounts and imports tab. Everything there is really self explanatory.
If you're using your AT&T account for responses you may need to set up your password on your phone too. I don't, I simply use gmail on my two POP3 accounts so they all come in as Gmail.
In order to sync your contacts I believe you will have to purchase The Missing Sync. It cost about 40.00. I'd look around first though, there may be a free one out there. I believe I have read about it in this forum
Hope this helps out.