How can i change the service on a sprint phone to sprint samsung instinct?

I heard that you could call customer service to do that but, when i got my phone they told me that if i wanted a samsung instinct i would have to add a data service to my plan so i got another phone. If i buy a samsung instinct from someone do i still have to get the data service?How can i change the service on a sprint phone to sprint samsung instinct?you have to get the data service if you want to run the internet and e-mail. But if you are just using the phone for just a phone than you dont even have to talk to anyone. Go to sprint.com and you can transfer your phone online. its easy and takes 10 minutes. and you dont have people pressing you to buy other plans