IGN has the details -
http://au.wii.ign.com/articles/819/819583p1.aspx this is a very big mistake if not remedied soon. Battalian Wars 2 with Co op but no online chat? MoH Heroes 2 with 32 player online with out the means to communicate with fellow team members? Very dissappointed.
I expected being so late to the online party they would get it right when it was finally released to the public, but it still not complete. Its not a deal breaker for me but it is still disheartening news all the same. I hope either Nintendo addresses this problem soon or online games on Wii can be later updated to support online chat.