Mac Mail Problem

Can someone explain to me why I was able to set up my Yahoo! mail account with no problem on my iPhone 3GS, but it seems impossible to do it on my MacBook? I've tried every variation for the incoming server, but it always tells me something about Yahoo! Mail Plus charging.. but my account is not Yahoo! Mail Plus, and it works perfectly on my iPhone.

And I'm also having trouble setting up my school email on both my phone and Macbook. It's an OWA/Microsoft Exchange account.

Any help would be appriciated. Thanks.

Have you enabled POP in yahoo

No, it says I have to upgrade to Yahoo! Plus for that.
But why will it work on my iPhone and not on my Mac?