I have an iphone4 and a Blackberry which I'd like to use interchangeably whenever I want. Right now, I'm using my iphone4 with an unlimited data plan from ATT. I was told by the ATT cust.rep that if I want to use my BB, I should go to the ATT shop so that they can switch my plan to a BB plan, or else I'll be charged extra fees for every time I use the data. And vice versa. A friend told me that in order to avoid this 'troublesome' issue, I should just stick to BB unlimited data plan and then I can use the SIM card on both phones, as long as the iphone4 is unlocked. I have a factory unlocked iphone4 which I bought from Canada. Anyone ever tried this before? I don't want to be slapped with an insane amount of bill if I were to use my iphone on a BB data plan. As for the size of the SIM card, I have micro-sim card adapter, so that won't be a problem.