I'm not an AT&T customer. So instead of giving you an advice, I'll just give you links to expert and customer reviews. I hope this helps :)
http://cell-phone-providers-review.toptenreviews.com/cingular-review.html
http://www.cellphonebattles.com/att-wireless-service-review/
http://goingcellular.com/reviews/att.html
http://www.epinions.com/reviews/General_Reviews_of_AT_T_Customer_Service