How to disable call forwarding options? [Solutions within]

[Globalize]

I have various call forwarding options within my Android phone, they are as follow:

1) Always Forward

2) When Busy

3) When Unanswered

4) When Unreachable 

I would like to use 4) When Unreachable only, but options 2, 3, and 4 are enabled by default. I was wondering if anyone knows how to disable options 2 and 3? When I clicked the "turn off" button by tapping the individual options, I get a "Call settings error - Your operator doesn't support disabling call forwarding when your phone doesn't answer". Is anyone else getting the same thing as me? 

The reason I am asking because I have my Fongo number setup for "When Unreachable" and do NOT want my Fongo number to ring when busy or unanswered. I could just simply change the number associated with the options 2 and 3, but that would lead to another number ringing. 

EDIT: Ahhh after playing with the phone settings, I have discovered how to achieve this. The solution to turning off the individual options is to delete the number associated with the options and click update, you will receive a "call settings error" specifying unexpected response from network. Then that respective option will be grayed out, indicating it is now off. In addition, if it shows a forwarding number of "15875884001", this means the option is now off. (You may get a different forwarding number shown there). 

[WearySky]

Note, this is how voicemail works.  The number shown there by default should be the voicemail access number for your phone (different access numbers for different area codes - are you sure yours isn't 587-580-4001?  That's one of the 587 voicemail numbers according to this thread).  That's why you can't turn it off entirely (and it's also how you would use a third party voicemail provider like YouMail, if PM properly supported OCN right now).