I just found out that we have Call Forwarding issue with our CUCM. I can not call forward the phone from the CUCM admin.
After i setup the call forwarding in the CUCM, the phone changes and re-registered, then the phone screen is showing that the phone is forwarded to the forwarded number.
but when i call it, it is still ring to the phone, then to voicemail as the phone is not forwarded.
But when i forwarded from the desk phone, It works and i can see the number is filled in the CUCM admin page (Destination).