At http://ypops.sourceforge.net/modules.php?op=modload&name=Sections&file=index&req=listarticles&secid=1 you can find a handy application that will allow your email application to upload and download Yahoo! email. I use Outlook 2003, but there are instructions there for many different apps and platforms.
I haven't tried it yet; I just found it, and I'm not on my primary Outlook-bearing PC, but I'll give it a try and post the resutls.
How low will we go? Check out Yahoo! Messengers low PC-to-Phone call rates.