How much will a iPhone 4s plan be?

My Friend Is Gonna Give Me Her iPhone 4s Because She Got An iPhone 5. The iphone is either Sprint or At&t. I'm 16 years old & ill be starting my job in mid april. After i get the phone i'm gonna use it like an ipod till i get money to pay a bill. How much is it for just Call & Texting?

For Sprint, it would be $80 a month, before taxes and fees and such for unlimited mobile to mobile calling, unlimited texting and unlimited data (while on Sprint towers only).

For AT&T the cheapest plan is around $80 a month before taxes and such for 450 minutes, 300MB data and unlimited texting.

Both AT&T and Sprint (as well as Verizon and T-Mobile) require a data plan for a smartphone such as the iPhone.