UPDATE: WORKS!!!! Is there an AUTO - Data Disconnect regedit?

[Fixup]

I cannot see why this registry mod will block incoming calls, it'll only allow calls coming. Here is a little more details about data connection and call block:

If data is EVDO or 1X, calls won't be blocked, even if data is connected.
If it is connected over 1X (not EVDO), calls are blocked if there is a data activity going on.
If it is connected over QNC, calls are always blocked, regardless data activity.

If data is disconnected, there is no reason for call block. Something else is wrong on you your phone.

If you have set up an exchange account and set it to pick up as items arrive, the data connection will be always resumed. So will if you have other push running such as ImapPusherService.