cluelessinWpg, if you are an existing MTS internet customer who signed up before August 17th, and still haven't migrated your email to windows live, you can still use the "pop.mts.net" and "smtp.mts.net" server settings in Apple Mail. It's not difficult to set up, but if they're phasing out their in-house email, there might not be much point.
But if you still want to, read here
on how to do it. (Their page says it's for 10.3, so it'll be slightly different if your Mac is new.) I don't remember if Mac's are shipping with Snow Leopard (10.6) or just Leopard (10.5) still
If you're MTS account is already through Windows Live, read here
on how to set it up in Apple Mail.
My personal suggestion would be to forget about MTS email. I know that's easier said than done, especially if everyone has that address. If you ever cancel your MTS internet (regardless of it being before OR after migrating to Windows Live) you lose that account, so why not just abandon your ISP's email address and setup your own Windows Live (or gmail, etc).
I have my Gmail setup in Apple Mail, but as IMAP instead of POP3. I have to say, it works pretty slick compared to POP3, which is more of a one-way service. I had to fart around to get it working just right. Apparently there are some extra tweaks
that the Gmail team haven't figured out yet.
EDIT: forgot to mention that yes, you can setup Gmail to retrieve POP3 emails. It will only stop working when MTS shuts down their in-house email servers (I forget when) at which point you could migrate to Live and modify Gmail to Live's server settings.