All phonecards are changed in incremental billing periods or blocks. The size of these blocks vary. Some phonecards charge in one minute blocks/increments, 2, 3, or 4 minute blocks etc. If a phonecard has 3 minute blocking and you make a 4 minute call you will be charged for 6 minutes. If you want to make several short calls with your phonecard pick one with low blocking periods (1 or 2 minutes) if you want to make one continuous call then pick one with higher blocking periods, but make sure you are aware of what they are. If you can't get though or a answering machine picks up make sure you disconnect the call straight away.