WiiSpeak microphone box and discovered the secret behind the associated Wii Speak Channel: it's a free download, yes, but that download requires the entry of a one-time-use code included in the box. At first blush, this isn't a big deal, because anyone who wants to use the Wii Speak Channel is probably going to have a microphone anyway, right?
The problem, as Totilo identifies, is that you can't buy the thing used and expect the channel, because the "Download Ticket" will have been used. And Nintendo won't replace it. The channel won't be available for purchase, or for free download without the ticket. So buy the thing new or plan to chat only in games.