v20 call forwarding

[i3]

In v18, I had created a dummy extension, 123, which had the conference ext + conference ID (123*400*) as the mobile number. I then set the extension to forward to mobile number. When ext 123 was dialed from internal or from an IVR, the caller would automatically be put into conference room 400. Now it seems the system is attempting to route the call externally and thus giving me the no route error. Is there a way to re-create this functionality?