Does the wii have buddy lists like the 360?

No, the online options of the Wii are very limited, especially when compared to Xbox Live. Check it out for yourself...

You'll have to call them on the phone.

The system does use a 'friend codes' system witch is system based (thankfully that rather than per-game like the ds) and when you trade codes with someone you can send messages back and forth (if you link together with someone's email address you can send email back and forth through the wii) so it's not to the level of xbox live (nothing is really) or even the ps3 but it has a bit of something (the first actual online game coming out this month, being a pokemon title)

But to again stress the answers to the original question...

No, you can't directly determine when other players are online or what they're doing.
No, you can't chat with them or send them voice messages, although you can send e-mails.

But he asked if there was a way to tell if his buddy was online. I think once they swap friends codes, he can tell if they are online. That was what I understood from watching a demo of a developer playing Mario Strikers online. It looked like he pulled up a list of his friends and it said if they were online or not.

Again, this was just from watching a video, so I could be mistaken. We need someone from the UK who has Strikers and has played it online to verify.

It may be possible to tell if the other player is actively in a game which supports multiplayer online play, but it's probably not possible to tell if the other user simply has their Wii turned on. Remember, the Wii doesn't really seem to have a unified online strategy, so the concept of having a "friends list" that one can pull up during a game would probably be implemented on a per-title basis.