It depends on the plan you're currently on. If you are on an individual plan, i.e., with only one phone, you will need to switch to a family plan. If there will be only the two of you on that shared plan, the second line is free. If you are on an older family plan with already 2+ lines, then most likely the line for your daughter will be $9.99. If you are on one of our current talk or messaging plans, it will also be $9.99. If you happen to be on a data plan, it's $19.99/per line for lines 3-5. Please see http://community.sprint.com/baw/servlet/JiveServlet/download/220909-38785/Rate%20Plan%20Your%20Savings%20Charts%20as%20of%20August%202010.pdf, page 2 for current family plans.
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