How much will an iPhone cost per month?

I am still on my parents family plan with AT%26amp;T and we have the unlimited $30 family texting plan included. I was wondering how much will the data cost for an iPhone (I am planning on purchasing one in June, the new one if one comes out, the 3Gs if not). Is the data plan $30 or can I use the unlimited family data plan for $10 or the other data plan which costs $15? Also, what are the chances of a new iPhone in June?|||i have the iphone 3G and im with rogers and i pay 62 dollars a month and i have unlimited texting and its actually unlimited and thats also picture and video messaging. i have unlimited evenings after 6 and weekends i have 500mb of data which is a lot. ! lol im always online on my phone and i never go over. and i have the my5 plan on top of that but it works out to be 62 dollars. they are not very expensive at all i had a crappy phone from koodo and my bill was always like 77 dollars and higher im paying less with my rogers iphone then i was paying with a crappy koodo phone lol. ! hope this helps :)