Here are the codes to activate call forwarding function of your dataport mobile number:
Call forwarding to:
Forward when busy: **67*$NUMBER# and then ✆.
Forward if you don't want to answer: **61*$NUMBER# and then ✆
Forward if not available (cell phone off, no reception): **62*$NUMBER# and then ✆
Always forward immediately: **21*$NUMBER# and then ✆
Disable all O2 call forwarding/mailbox: ##002# and then ✆