You can put the sim card into your blackberry, BUT it wont work with data until you call and tell them you have changed to a blackberry... unless you are a new iphone user the old iphone unlimited data plan cost the same as the blackberry data plan so there will be no charges, just call let them know and vuala
Actually, you can get data, but not using BIS or BES. You would just use the regular settings for AT&T data. I don't recall off hand, but I think you set it under TCP/IP in the advanced settings. Also, you have to set the browser to "internet browser" and not "blackberry browser".