It looks like the Wii Speak channel will only be available to those who purchase the microphone.
The channel acts as a bridge to those that use the microphone, allowing free communication over the internet. Back in their fall conference, the company revealed that it'll be freely available to those who purchase a Wii Speak mic (or receive it bundled with a game):
The channel will be free to those who have purchased the Wii Speak peripheral (via a code) for an MSRP of $29.99.
It now looks like this would be the only way of grabbing hold of the channel as Nintendo has told MTV Multiplayer that buying a new Wii Speak microphone will be the only means.
Those that buy a used microphone will most likely not be able to use the channel, nor would possibly third party alternatives be able to benefit from it. Fortunately a large quantity should be available to compliment the release of Animal Crossing: Let's go to the City, but such measures should really not have had to be taken.
A ridiculous move from the "consumer-friendly" Nintendo?