How much is an iPhone bill monthly?

Hi, I've heard things like it is crazy expensive a month. What I'm planning on doing is getting the iphone 5. From someone I know, they said they only pay 40$ a month. I wanted unlimited data, and texting, plus it would be on a family plan. How much would that cost monthly?

Iphones don't really have unlimited data, but if its att its about 40-60$ depending on all added stuff or jut plain out regular phone bill. I only know for att tho:/