Prepaid international calling cards are billed in increments. These increments don't refer to the denomination of the prepaid card but to the call billing.
There are several types of phoncards:
Let's take a prepaid card with 1 minute rounding. If you call for 1 minute and 2 seconds the call will be rounded up to 2 minutes. If you place a call using your calling card for exactly 2 minutes then you will be charged for only those 2 minutes. The phone card bills you in 2 minutes increments
Same thing applies for a calling card that has a 4 minutes rounding. A call for 2 minutes 30 seconds for example will be rounded up to 4 minutes. A call for 8 mintutes will be billed as 8 minutes, but a call for 8 minutes and 1 second will be billed for 12 minutes. This time the calling card bills you in 4 minutes increments.
Usually phone cards companies will display all types of calling cards. You will notice that the smaller the rounding the higher the rate per minute for the calls.
Calling cards with a higher rounding are usually associated with another important detail: maintenance fee
Then what should you choose: a calling card with a higher rounding or a calling card with a smaller rounding increment?
The answer to that question lies in just one factor. How long your calls are.
People who tend to call for more than 20 minutes for one call should go ahead and purchase calling cards with a higher rounding. It's because that tipe of calling card WILL have a lower rate per minute to their destination.
People who place shorter calls should buy calling cards with a smaller rounding. Because the rate is higher but the billing more accurate they won't loose minutes because of the calling card rounding up to the next interval.
Before going to the top calling card companies, please take your time to read also the rest of the material on calling cards details:
CALLING CARDS MENU PAGES
TOP long distance calling cards providers
USA (United States) ---> 0.8¢
INDIA ---> 8.3¢
UNITED KINGDOM ---> 0.95¢
CANADA ---> 0.89¢
ROMANIA ---> 6.40¢
GERMANY ---> 1.33¢
RUSSIA ---> 2.40¢
AUSTRALIA ---> 0.90¢
BULGARIA ---> 2.40¢
PAKISTAN ---> 7.00¢