Ditto to above....
Exactly the same is occurring on brand new iPhone 5s - which I just received and set up yesterday.
To add to the weirdness - I have a pre-paid T- Mobile Plan which does not even include call-forwarding at all. I've checked with them; they say it's definitely an Apple software issue.
Apple tech support say restoring to factory settings is the way to try to correct this problem. I'm unwilling to do this at the moment - as I've just invested too much time in setting up the phone (only yesterday). They say I'd definitely lose many of these settings - including special DNS number strings which I've added to my Network settings, passwords etc......and would have to set them all over again
I've tried the solution suggested in this thread and what's been suggested on the AV forum website, where the issue was also addressed....
When I go to Settings/Phone/Call Forwarding.....and then add either my land line number or even my Google Voice number - it makes no difference - the icon reappears when I turn on phone again, after having completely shut it down.
And yet, when I then return to settings after the phone "re-boot" - it shows it to be turned off. And, as before, the act of going there - serves to remove the icon.
And btw: If I hit the back button immediately after entering my landline or Google Voice number....although it shows call-forwarding is turned on (the button is now sort of grey-green (like it's on but not on)
and....the above occurs ad nauseum.........
Any ideas anyone??????