So I have an AT&T iPhone 3G with the data plan. I very much like the phone, but I need a blackberry for work (we use their corporate email nonsense). Ideally, I would like to be able to switch my data plan from an iPhone data plan to a Blackberry data plan and receive the BB perks such as BBM and push email, etc. Does anyone know if I would be able to swap my sim card between the two and use the BB on the weekdays and the iPhone on the weekends? Also, if I use data on the iPhone with the BB data plan, would I be charged for extra usage? Thanks for your help in advance!