It's only in certain areas right now if I'm not mistaken. Also I've read that someone said you have to be on mobile share data plan for it to work,this I don't know is true or not.
I activated mine last night. I'm in Orlando Fl with mobile share if that helps
AT&T rolls out features by market. Not all markets get things at the same time, prime example is VoLTE. Atlanta had VoLTE for a while, while for me in SFL we got it like a month or two ago.