here's instructions from
this thread
HKLM\SOFTWARE\OEM\PhoneSetting
Change the option HiddenModeOperationPage from 1 to 0
Then go to Phone/menu/option/service/and check in the list, "Mode of Operation" should be at the bottom. You have 3 choices, Hybrid, EVDO, and 1X.
also look @ the DDTM option in there too.
@bunny I'm not sure you want to force the phone to kill the data connection on every sleep. primarly I think it could lead to sod's since it takes a few for the connection to terminate. as long as it's killing via the timeout then your fine.