In your station class of service, is your phone allowed to forward?
I am not 100% certain how to verify this, but I presume the fact my phone can forward to my cell phone when I have the speed dial setup as that it can.
Are you testing the speed dial manually from the phone you are wanting to forward from or a different phone?
Yes, I can leverage the speed dial from the phone I'm setting to forward. And the forwarding works flawlessly if I made the speed dial my cell phone number. Just fails to work once I put in the Cisco extension and does the dreaded "3" on the display and busy.