How much is an iphone data plan?

My brother and I are both getting iphones and my parents are staying with there old phones which don't have internet or anything so could you have two smartphones and two regular phones on the same plan and how much is the smallest but still useful data plan for an iphone?
other info our current plan has unlimited text and 1500 talking minutes for the whole family would the price for the talk and text go up for the iphones?

Added (1). The phones are on sprint

You can have them under the same account but they have to be on differant plans because each phone has a sepperate SIM card… The cost of the plan depends on the carrier and also the ammount of calls, texts and Data you want xD

First off all, don't go with Sprint.

Go with Virgin Mobile USA. They are a SUBSIDIARY of Sprint, so you'll have the same service.

Here's the deal, with Virgin Mobile USA, you pay only $30 dollars a month for 300 calling minutes, unlimited texting, and unlimited data. You'll save truckloads of money switching from a Sprint iPhone to a Virgin Mobile USA iPhone. You'll have the same service but be paying much less.

www.virginmobileusa.com/iphone

I'm not trying to market for Virgin Mobile USA, i'm trying to save you money! I have Virgin Mobile USA - like I said, they run off of Sprint's towers - you'll have the same service but you'll be paying much less! Just trying to save you money!

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