If i get a prepaid phone from tmobile do i have to add the phone to my dads account?

[x_RSP_x]

I need phone and my dads cell phone bills too high so im geting a prepaid cell from tmobile. If i getone do i have to add the line or whatever to my dads account to pay for minutes. If i had too does that mean i can get unlimited texting because my dads paying 20$ for the whole family and im added. If not what ever. Please dont tell me which other phone servicesare better. Thank youu