[Aleki]

While it will get rid of the data service, anything that tries to connect will bug the crap out of you with login information. To do this go to:
Start/Settings/Connections/Connections/Manage existing connections. Under the modem tab, there should be radio buttons that show your provider's name, and in some cases, phone as modem, or other services. The number that displays right next to the name of the service is what the phone dials out to attain a network connection (deleting the radio button will only cause it to reset the information when your phone attempts to reconnect). You can change that number by highlighting the radio button and tapping edit, and keep tapping next until you get to the option that allows you to change the number (#777 for sprint). Change that number to whatever random number you feel and continue tapping next until you go through all the options. After youve changed that information, you may need to do a soft reset so the phone will dial out to the new number. If you ever want to revert to allowing the phone to use data, go back to the settings and either re-edit that number or delete it (it will regenerate with the proper information if its the only radio button on the field).

If that confuses you, let me know. I'm not in the right state of mind to do a proper writeup