i dont think thats true, im using my old 3GS's sim on a 5 year old ericsson and i still have my unlimited data plan.I don't even have an iPhone right now. I sold mine on eBay last Sunday night hoping Steve would say, pre-orders today, available this Friday. Whoops. I've been forwarding my AT&T calls to my Sprint Blackberry. My life sucks right now.
AT&T told me if I put the SIM card in another phone I'd lose the Unlimited Data. I wasn't about to do that. So forward the calls, and that's it for now.