If you are an AT&T customer, there is good news on the horizon; your phone bill will go down. Unless you are a heavy iPhone user, that is.
AT&T is introducing tiered pricing for iPhone users. (Read article here.) The lower tier is for people who dont use alot of the data functionality of their iPhone. These people will see a low to modest reduction in their billing.
The upper tier is for people who use more than 2GB of data per month. These prices are designed to cover the cost of lowering pricing for everyone else.
So you can expect to pay modestly to significantly more than you are now.
In case you are wondering how much is 2GB per month, Comcast reports that the average Comcast customer uses about 2GB per month for email alone.