Taken from the vodafone website (actually inside a PDF file rather than just web accessible)
Diverting calls to another phone
Please see below details on how to divert your calls to another phone.
Divert all calls to another number:
To activate – enter **21* then enter the number you want to divert your calls to – replacing the first 0 with +44 followed by # (eg: **21*+447747123456# ) then press Send.
To cancel – enter ##21# Send.
To check set up – enter *#21# Send.
Divert missed/unanswered calls to another number:
To activate – enter **61* then enter the number you want to divert your calls to – replacing the first 0 with +44 followed by # (eg: **61*+447747123456# ) then press Send.
To cancel – enter ##61# Send.
To check set up – enter *#61# Send.
Divert calls when your phone is busy:
To activate – enter **67* then enter the number you want to divert your calls to – replacing the first 0 with +44 followed by # (eg: **67*+447747123456# ) then press Send.
To cancel – enter ##67# Send.
To check set up – enter *#67# Send.
Divert calls when your phone is switched off:
To activate – enter **62* then enter the number you want to divert your calls to – replacing the first 0 with +44 followed by # (eg: **62*+447747123456# ) then press Send.
To cancel – enter ##62# Send.
To check set up – enter *#62# Send.
To cancel all diverts:
Enter ##002# and then press Send.
