$40 for voice, $30 for data, $10 for text, plus taxes and fees. Around $90 total. That's 450 minutes. If you need 900 minutes add $20. That's 2GB of data. If you need more data, add $20.
Assuming the plan you have with your BB is eligible (I came to the iPhone from a BB) then you would be paying the same amount you are currently paying (if you have the unlimited data plan then you will retain that). If you don't have texting now then you don't have to add it...if you want the hotspot feature you will have to pay for that (I believe it's an additional $20/month). Ultimately, if you're coming from a smartphone and switching to another smartphone your monthly fees should remain the same unless you add or change something about your plan.
I always thought it was 30 dollars a month for 2gb of data a month but I am very likely to be wrong. One other thing i would not recommend the iPhone I personally think you have way more abilities on an Android Smartphone. Just my view.