Using Siri to do call forward

Hi,

When I was using the Voice Command in my iPhone 4, I was able to enable/disable call forward by setting up a contact with the phone number something like **21*[tel no]#.

After I have changed to use iPhone 4S, Siri is unable to dial that call forward number. It said "Sorry [name], I can't call [the contact name] number." Something like that...

Any one has any clue to use this trick in iPhone 4S?

Or Apple is planning to include this command in iOS 5.1?

Please give me this function back!!!