Sure, its included, at 20 cents per message
According to the pricing on the AT&T site, text messages ar 5.00 for 200, 15.00 for 1500 and 20.00 for unlimited. Thats on top of the voice plan.
The rep was either just wrong or quoted you a price for the 1st gen phone which had text as part of the plan. But hey, try and get them to honor it. When I get reps that tell me those things I pretty much know is incorrect I ask them to make a note of what they said on my account, so when I call back, I tell the next person I speak too, to check the account notes.
Doesn't guarantee they will honor it, but can't hurt to try.