Question : Blocking unknown or private calls on iPhone 4

I am a blackberry user who is considering switching to the iphone 4, but i love the way I can handle "unknown or private calls".

Is there an app that will forward them to my voice mail or block them all together?

I don't want to call AT&T to try to block that way,

thanks

Answer : Blocking unknown or private calls on iPhone 4

Citrix is the best way to this, they have tied in tightly to the Mac - even the ipad and iphone.
http://community.citrix.com/display/xa/Citrix+Receiver+for+iPad
This a pretty cool video showing how they allow you to use your iphone as a mouse track pad for the ipad! Crazy!
http://community.citrix.com/display/ocb/2010/04/09/Citrix+Receiver+for+iPad+-+Demo+1+-+Wireless+TrackPad