iPhone iOS 6 upgrade - no call waiting
After upgrading my wife's 4S to iOS 6 she can no longer answer any call waiting calls. If she is on a call, she can (only sometimes) hear a beep that another call is trying to come through, but nothing shows up on the caller ID and there are no options to switch or ignore the call. The call doesn't even show up in the call log.
I upgraded my 4S and I do still see call waiting options, but they don't show up on her phone.
Any ideas?
Also, I checked, and under Settings-->Phone there are no longer any options for Call Waiting or Call Forwarding options. They are not present on mine either, but my call waiting still works and hers doesn't.
iPhone 4S, iOS 6