If you lived Ontario - West, 7-Eleven is the cheapest way to go. My wife needed a low use phone, so last September: I bought $100 in air time (@ 20 cents a minute local, 30 cents long distance) you got a phone for free, and the minutes were good for 365 days. 99 cents a month for 911 fees.
Petro Canada http://retail.petro-canada.ca/en/independent/2321.aspx
uses the same company as 7 - Eleven and has the same rates. You can use petro points to buy the phone and the minutes. But, not as good of a deal as 7-11. The cheapest phone is $60.
I also have a virgin phone, but the per minute rate is 30 cents local, 50 cents long distance, and minutes last 365 days if you buy $100 worth. No 911 fees.
Superstore/ Loblaws has prepaid phone service as well. Their phone can work in the states, but it is like $2.50 / minute.
The yearly cost is higher, $25 for 60 days x 6 = $200 /year. When you roam with your PC mobile phone in the USA, the following charges apply: $1.80 CDN/min for airtime if you make a call to anywhere within the same US local calling area where you are physically located. Additional $0.99 CDN/min for any long distance calls you make outside the US local calling area where you are physically located. Both of the above charges ($1.80 and $0.99) apply to all incoming calls, while roaming in the USA
If you don't use the phone in the US that much, I suggest a roll of US quarters and a prepaid calling card to use at a payphone.
Neither 7-11, petrocan or virgin work in the US. Some folks recommend you buy a 7-11 phone in the US or T-mobile if you are there enough.
Remember, any phone (with or without minutes left) will call 911 in USA or Canada.