It is something very difficult to do anymore...near impossible. You used to be able to simply move a sim card from a phone with out data service into an iphone and get away with it, but they are able to determine the type of phone you are using much better than before. The only AT&T supported way would be if you were able to get a manager approval before a specific date that has long since past, or if you had a documented visual impairment. The only way I have seen an iphone used without a data plan is by jailbreaking it and using it on a different carrier. If you have a phone with AT&T now and do not have a data plan, DO NOT swap your sim to the iphone!!! AT&T will AUTOMATICALLY ADD a data plan that you will not be able to remove.
-Anonymous