I had the ATT card for quite awhile. I was actually a charter member, this was when you needed something special to make a call using a credit card. Now I don't think it matters, most any credit card will allow you to make a phone call. But there was no annual fee, so I kept it for quite awhile.
Then I got a different card which doesn't charge hardly anything to use an ATM. Keep the ATM fees in mind if you think you may want to get a cash advance like that. ATT I think was going to charge me like $5 minimum for a cash advance. I don't use a credit card very often for this purpose anyways.
Good idea about getting one though. Maybe just use it for online stuff. Don't get in over your head with it. Don't buy anything you can't pay off that month, or maybe two months. If you pay it every month, then it doesn't matter what rate you can get, factor that in too. Make sure it's no annual fee.

Gilly