I'd imagine you'd have a bunch of cheap ones in the house that are all WiFi + Mic + Speakers, streaming back to your actual voice processing box (which would cost a wee bit more, but also have local access to all the data it needs).
You can see quite quickly that this becomes just another program running on a host, so if you use a slightly beefier machine and chuck a WiFi card in as well you've got your WiFi extenders.