From the Sprint Community forums:
Here are the instructions:
1. From the dialer, dial: ##DEBUG# (which is ##33284#).
2. Enter your 6 digit MSL. If you do not know your MSL, just get it from Sprint. It's not some kind of super-secret code that they try to keep under wraps, so don't worry. They will happily provide the number because Sprint has great customer service. They may ask why you need it. I told the representative that I wanted to program my phone.
3. From the HDR/1x Selection screen, select "CDMA Only Mode", then OK.
4. Reboot your phone
beliving tried this in an attempt to eliminate the data lockup when using wifi. Didn't work.
I'd say proceed with caution.
Late Edit: If you're using data in 1x (email, web) calls will go straight to your voicemail.