Nintendo has yet to announce how Wii users will communicate with one another. There has been no keyboard announced, and the few Wii interface videos that have been shown don't have a virtual keyboard. Personally I think it's a little late to announce a new periphal for a system that is going to launch in less than 16 days.
Also I was watching G4 today, and they were speaking to a Nintendo rep, and the interviewer asked they guy, how will the Mii's communicate? Text, or will little bubbles pop up over their heads? His answer was that there will be many communication features including the ability to use a message board, and leave messages for your friends, BUT, we're not revealing it yet, it's one more of those secrets we want you to wait for!
A keyboard is not a secret.
The other question is, why would Nintendo wait this long to announce such a vital part of the online strategy. It seems that besides gameplay all other features of Nintendo's online system will be available for use right out of the box. So it would seem that the method to communicate would already be included in the box. When we're this close to launch and no extra periphal has been announced it's safe to assume one of two things: 1. As discussed and much exhausted, the Wii-mote's speaker also includes a microphone. 2 Nintendo is going to piss off a lot of people by either using the one of the slowest on-screen keyboards ever, or announcing a new peripheral.
The biggest question is why keep this secret until now? Whatever the input method is, we have seen nothing of it. It's a little late for them to be worried about Sony copying their method as the launch of the PS3 is less than 2weeks away. They still owe us more details on Wii24Connect, but even that they gave a good amount of information already. However, something as important as the way we'll all be communicating with each other should have been revealed, unless it's the simple act saying that the controller also has a mic, which for the sake of making sure there are no riots, I hope it is.