How do I disable the message "Conditional call forwarding is enabled"

Hey WangYcca, 

I don't have the Xperia but try this : 

Enable Conditional Call Forwarding:

1. Open “Phone” and tap “Menu”
2. Access “Settings”
3. Go to “Call forwarding”
4. Select to forward incoming calls “When unreachable”, “When unanswered” or “When busy”
5. Edit or enter the phone number you want to use
6. Tap “Update” / “Enable”

Disable Call Forwarding:

1. Open “Phone”
2. Tap “Menu” > “Settings”
3. Go to “Call forwarding”
4. Select the forwarding option you want to turn off and tap “Disable”

Hope it helps