how much would my phone bill go up if i upgraded from a basic phone to a smart phone? ALLTEL*?

i plan on upgrading my basic phone to a smart phone within the next few days, and i would like to know how much more my phone bill is going to be. im not getting an iphone since i am with alltel, it will probably be a galaxy 2. they are free at alltel, and i have an upgrade available. i just need to know how much more my bill will be?
AVDADDY- because i MAYBE i wanna know before i go down there, i didnt ask for your smart ass answer..