This isn't true. When you deactivate the data plan you simply have no internet when not around WiFi. You need to tell the CSR to put you on the pay as you go plan to pay per KB.
You may want to double check that. The data plans allow you to use the network for a set price. Any other use is charged as per use. This is similar to not having a text messaging plan. Any texts you send or receive are charged per use. I didnt have a data plan on one of my previous phones with internet capabilities. I used it and ended up running up a data usage bill. Things may have changed since then but I doubt it.