I'm upgrading from a 3g and have the minimum required service for that phone. I'm wondering what the minimums are for the iPhone 5 and what the charges are? I don't make many calls, I text under 200/month and I am a moderate browser. Right now, I'm paying in the mid $50s. How much will my bill go up?
AT&T typically allows you to stay on the current plan when upgrading, so it's very likely that unless you yourself request changes to the plan your bill will stay the same.
Delineate what you are paying for each feature. Your costs seem to be rather low considering that the lowest priced voice plan is about $40 and the lowest grandfathered data plan is $15 for 200 megabytes. Are you on pay per use for messaging or one of the older limited messaging plans?