I'm not sure if that option is available yet but why would you want to?
What function of the Superhub 3 do you feel you need that is not currently available on the 2ac and what facilities that you are using today would you be willing to lose on the current Superhub 3 firmware?
Because some people have an SIP phone and the Super Hub 2 has a problem that is a pain in the ass to fix (It may not even be fixable) and some people hate the super hub 2 because IT IS GETTING SLOWER! (Like mine, that piece of **bleep** can't do much anymore).
I want a new fast Super Hub that is fast and quick that is also reliable, I am tired of these bad quality that will break down in a month or 2