i would guess that the rom you are using does not have the sprint customizations built in. if they are in your extended rom then you will need to find the sprintcustomization.cab and run it again to install the ## codes. also run IOTA.sa.cab and that will reinstall the ability to request iota from sprints network.
If you install the 2 cabs and power the radio off for 60 seconds then back on agian. then go to the phone settings and select the service tab. then locate internet, tap get settings, tap start. you should see IOTA appear at the top of the screen. you can tap OK to exit the settings menu. in about 3min you should be connecting without problems.
if you try to connect and it asks for username and pw just place a check in save password and tap ok.. you should be browsing in meer moments.
if you get the ## codes working but still not able to IOTA then go to ##3282 or ##778 and program your vision username and pw manualy. your username is you sprintpcs email address, if you do not know your password you can set a new one on your manage page at sprint.com.
good luck