I can't speak for AT&T but we have been doing the same thing with Verizion for the last 3 years. Way better than dial up on our old phone lines. No options for cable or DSL. We should be upgraded to 4G by the end of the summer and that should make it even better.
We are light weight users and get 5 Gigs per month for about $50 per month. If you are a heavy user and down loads movies and such, be sure to check the cost of going over the monthly limit. I got hurt one time with that. Verizion has a mobil hot spot that is good for 5 devices at the same rate. We have found that useful. I'll guess AT&T has something like that.
MarkV