The mic in the Visor is not connected to any Visor electronics. It is connected directly to the Springboard slot. It can only be utilized by Springboard modules, i.e. the aforementioned phone module; voice recording modules, etc.
There is No Way to make use of this mic through software, it just isn't attached to anything inside the Visor.
A bit of a tease as-is, in order to use it you Must buy an appropriate module.
--Stephanie