Seven Eleven in Canada now has inexpensive prepaid calling for iPhones (unlocked GSM or unlocked CDMA) with SpeakOut Wireless. The SIM card is $10, and you also buy however many minutes you need. This is a voucher receipt you get from the cashier at Seven Eleven. I bought $25 worth from the Canadian Seven Eleven store. Once you have your SpeakOut SIM and your minutes voucher, you need to activate the SIM card online at SpeakOut Wireless. At their web site; setup an account with SpeakOut, enter your iphone’s IMEI number (Settings > About) and choose your desired location for your local Canadian phone number. If the SpeakOut cellular network is not displaying in the upper left corner of your iPhone after inserting the SIM, then you might need to restart your phone a few times to get the SpeakOut network established.
Note that SpeakOut’s SIM cards do not have the extra-small micro punch-out size. So if you have a newer iphone (4/4s), you have to shave it down to the micro size.
To activate the minutes you purchased, dial *818* plus the voucher number printed on your receipt. If you need additional minutes, buy more at the Seven Eleven store.
This SpeakOut prepaid solution does allow for data, but you should probably use WIFI while traveling in Canada, so turnoff the Cellular Data setting at the Settings > General > Network.