Why are the plans for the iphone so expensive?

http://www.wireless.att.com/cell-phone-service/specials/iphone-info.jsp

-That’s the plan for a iphone 3g.

http://www.wireless.att.com/cell-phone-service/cell-phone-plans/family-cell-phone-plans.jsp

-And that is the plan for normal phones.

The family iphone plans are practically double in cost compared to the regular family plans.
Why are the plans so expensive?

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