I've been experiencing this problem quite randomly. I've asked some friends around who have Android phones as well and this happens to them as well, so my first thought was that this is an issue with Android.
I try to call a number, and without ever hearing it 'ring' anytime, I get a Conditional Call Forwarding Active
message and a small beep, and it hangs up. I then re-try, and sometimes the call goes through, sometimes I get the same message. Sometimes, on occasions I have to try 4 - 6 times to be able to make the call. On very rare occasions, everytime I try I keep getting the message, beep, and hangs up. This is extremely frustrating. Any idea how I can look into this?
My phone is a Samsung Galaxy Note 2, stock Android (4.3 as per latest update).
Update 1
This has nothing to do with Call Forwarding apparently. I've disabled it from the Call Settings, and now it still happens, without showing the Call Forwarding activated
message.