Catfisman reported in his blog that MSN Web Messenger did not work on Nintendo Wii, but looks like eBuddy Mobile works fine :

"While messing around with the updated version of the Opera web browser for the Nintendo Wii, I decided to see if Microsoft’s online version of Messenger, Web Messenger. would work on it. Well, as to be expected, it didn’t work. I got a message saing that my browser blocked pop-ups and that I had to enable pop-ups for it to work (not an option).
...
Well, I decided to do a quick search on Google to look for alternative’s to Microsoft’s online Messenger, and I found eBuddy Mobile. I only tried Microsoft Messenger (as I do not have or use AIM or Yahoo’s Messenger), but I was happy with the results. "

Just point your Wii browser to http://www.ebuddy.com/mobile/ and use MSN, AIM or Yahoo Messenger Mobile.

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