Big Daddy,
I'm not from Canada, but TKO is right you can get prepaid phones at Futureshop (Bestbuy to us Americans) or at a lot of other places. Here in the States you can even get them at 7-11 (a convenice store chain). The phone itself is the big cost though, you might be able to do it cheaper if you already have a phone.
Here is the info I can offer you. Your phone number and bill are tied to the "sim card" chip inside your phone. You can use a prepaid "sim card" in the same cellphone if you already have one, but there are some restrictions. The cellphone service providers (Rogers, Fido, etc.) lock the phones so that they only work with their branded "sim cards". They give you the phone at a discount and they don't want you switching to some other provider and keeping the same phone, but it can be done. A Fido prepaid "sim card" should work right away in your phone, if it is also a Fido phone originally. Just turn the phone off and swap the "sim cards" (behind the battery most likely) and restart it, now you have a whole new number and the calls won't go to your regular cellphone bill.
If you want to use a different providers prepaid card in your phone, it is more complicated. You must have your phone "unlocked" from your original service provider, don't worry it will still work fine, it will just accept other "sim cards" without complaining. Depending on your current phone and your current providers rules it could be free and painless, or it could be a bit of a challenge. My provider here in the States (T-mobile) will unlock your phone for free if you have been a customer for over 1yr in good standing. But, you need to call up their customer service number and ask for it explicitly (most providers are not this generous here in the USA, but it never hurts to ask). Some phones you can unlock yourself for free (many older Nokias) others you will probably need to pay a few bucks. If you can't do it yourself, it can be done online through some websites for a reasonable fee or you might have to take it to a local cellphone shop in person (not where you bought it most likely, try Chinatown I would guess or some other independent cellphone shop). Once unlocked you are ready to go with any "sim card".
If you need more help with this, feel free to PM here and I will try to help you as best I can.
SOX