Absolutely... if you have coverage.
For the longest time I was on a Verizon family plan and was worried about switching to AT&T because of the additional cost (single line instead of family) and the suposedly horrible coverage. I got freaked out by all the horror stories posted on the web regarding AT&T.
A piece of advice: Ignore the horror stories. People with no life enjoy ranting about how crappy their service provider is just so they can feel superior. People feel entitled when in reality they are not. Yes, you'll find a lot of bad stuff written about AT&T on the web, but the same goes for any other carrier. All that matters is whether it works for YOU in YOUR AREA.
AT&T's coverage and customer service has been spectacular. Signal is not great when you leave metropolitan area but, honestly, why the hell should I base my purchase on if my phone works at my cabin. Coverage is overrated... if you get excellent service on a great device 90% of the time, thats far better than a carppy Verizon phone with 99% coverage. It works when I need it.
Go for it. The iPhone is amazing and absolutely worth the money. If all else fails, AT&T has a 30-day trial period.