well, normally it is auto-disabled on 2.0, but here you go:
SSH into your iphone and go to /System/Library/Carrier Bundles/ and then the Carrier Bundle of the carrier you use (so if you use an AT&T simcard go into ATT_US.bundle).
in there, download the carrier.plist and if you can't read it convert it using Convert Apple Property list from binary to text XML
after that, search for
<key>ShowCallForwarded</key>
and make sure the line below it says
<false/>
then look for
<key>ShowCallForwarding</key>
and, again, make sure the line below it says
<false/>
if one or both of those say <true/> change it to <false/> and re-upload the file to your iphone and there you go ;-)
enjoy
edit: if you don't know your carrier bundle just go to /private/var/mobile/Library/Carrier Bundle.bundle/ which takes you right to your carrier