A Nintendo rep has said that the only way gamers will be able to download the Wii Speak Channel is with a "Wii Download Ticket Number" that is printed in a pamphlet that comes with the Wii Speak microphone.
This apparently means that if you buy the peripheral it used, you won't be able to use it as you can't download the Wii Speak Channel.
To quote: But there's a catch, a fine print surprise. There is a pamphlet packaged with the peripheral that includes a 16-character code, a "Wii Download Ticket Number," to be used for downloading the Wii Speak Channel.
According to the pamphlet, this code "cannot be replaced by Nintendo or your retailer if it is lost or stolen." More PlayStation 3 News...