For many teachers, buying a cell phone SIM card at a convenience store is a great way to get started in our new milieu. Sold in 200 & 500 denominations, these little cards are pay-as-you-go: once you've used up the value of the card, just add more value to it, or - buy another one.
A second advantage of these pay-as-you-go cards has been the ability to survey all the steeply discounted rates among the various the independent long-distance carriers offer. Until very recently you could use the pay-as-you-go cards and access any discount carrier you wanted. If 016 was offering a great deal to Canada this month, just dial 016. The month after that, use 005 if it was best. That is no longer the case.
The cooperation between the convenience store pay-as-you-go cards and the discount carriers has ended. Have an IF Card, the pay-as-you-go kind you buy in a convenience store? The discount carriers available to you are 017 and 18881002. Have an OK Card, the pay-as-you-go kind you buy in a convenience store — the only discount carriers you can use are 006 or 005. With the Ideal Card, the only discount carriers you can use are 009 or 019.
If you are not using a pay-as-you-go card, then you have a phone and a number that you got by buying a brand-new phone and signing a contract with a cell phone provider. In this case, you have access to all of the discount carriers plans. Just check the right hand side of chart below and dial the prefix that has the best rate. (If you are calling from a home phone, you also have access to all the discount carriers - you need to sign up with them first, but it's easy).
Sticking with a pay-as-you-go card in your cell phone, you are limited to which discount carriers you can use.
In the chart, where you see two dashes, -- , that's peak and off-peak: