With wifi on and connected, will the 3G service never be used for data?

[Droid421]

Just found out what "unlimited" data means according to Verizon. If you don't know what I mean, have a look here:

Verizon Droid Tethering Will Cost You - Business Center - PC World

Anyway, with a wifi connection established, is it safe to say that my Droid will not transfer data over the 3G connection so I don't have to worry about this, or do I have to turn the 3G off and loose the ability to send and receive calls to know for sure that I'm not risking racking up more fees?

 

[murky024]

3G is still needed for visual voicemail... I think they will need to fix the feature that disables 3g when WiFi is on...